How much sleep do humans need?
Asked by: Martin Moore, Glasgow
The cliché is that we need eight hours a night, but the actual answer to this question is more complicated. Our sleep requirements change throughout life. Guidelines proposed by the National Sleep Foundation in 2015 recommended that newborns have 14 to 17 hours per night, teenagers have 8 to 10 hours, and adults have 7 to 9 hours. These guidelines focus largely on ‘average’ requirements, but individuals can differ greatly from one another. For example, it may be appropriate for certain teenagers to have as few as 7 hours per night, or as many as 11. If you’re not functioning your best, it’s worth considering whether you’re getting enough sleep.
What does sleep do for the brain?
Asked by: Sarah Cooper, Manchester
Too much stimulation of your brain cells can lead to neurotoxicity, which is dangerous, and so one tentative theory holds that sleep is a chance for the brain to enter a detox mode in which overall levels of neural excitability are reduced.
Sleep also helps the brain to learn, although the precise physiological processes that underlie this benefit are still being worked out. This means that after you’ve spent time revising or learning a new skill, it’s very important that you get a good night’s sleep. Doing so will help your brain to consolidate the neural connections that underlie new memories.
Why does depression make you dream more?
Asked by: Mary Benson, Lutterworth
People suffering from depression may experience unusual patterns of sleep. Typically, they move into REM sleep (the stage in which we are most likely to dream) more quickly, and there may be a greater number of eye movements per unit of time during this stage of sleep.
People who are depressed may wake up more frequently during the night, and are therefore more likely to remember their dreams. Finally, there is some evidence that certain medications for depression can increase the frequency of nightmares. Other medications appear to do the opposite, but nightmares can occur during withdrawal from these drugs.
How do circadian rhythms work?
As we are primarily active during daylight hours, our bodies have evolved a schedule for different metabolic processes to make sure we use energy in the most efficient way. Muscle performance and reaction times are optimised during the day, while tissue repair and memory formation are handled during our downtime. The circadian rhythms are the 24-hour cycles of each part of our body. They are controlled by the fluctuating levels of different signal molecules in our cells – known collectively as biological clocks. All the clocks are synchronised by a master clock in our brain called the suprachiasmatic nucleus, which is a group of around 20,000 brain cells in the hypothalamus.
Why don’t we fall out of bed more often?
Asked by: Lois Rumsey, Southwell
When we sleep, a lot goes on in our bodies. We continue to breathe and growth hormone is released – we do not need to be awake for these things to happen. Similarly, we have some awareness of our body position and movements, and some people even manage to sit up or walk during their sleep! Most of us have enough awareness to ensure that we do not fall out of bed, but this ability develops over time. Young children are still growing and understanding how their bodies fit into the world around them, which is why they might benefit from a bedrail.
What causes sleep paralysis?
Asked by: Mary Smith, London
During rapid eye movement (REM) sleep, our body is paralysed to stop us from acting out our dreams. When sleep paralysis occurs, features of REM sleep are continuing into our waking lives. In particular we are unable to move and sometimes experience hallucinations.
Both genetic and environmental factors are at play. Circadian genes might be important, although more research is needed to specify which genes are involved. As for environmental influences, it appears that anything that might disrupt our sleep – including stressful life events and alcohol use – can be a risk for sleep paralysis.
Why do we dream more in some places than others?
Asked by: Charlie Mack, Uckfield
Dreams most commonly occur during Rapid Eye Movement (REM) sleep, and are easier to remember if we wake during this stage of sleep or soon afterwards. Evolutionary theories emphasise the need to feel safe in order to lose vigilance and go to sleep, so we may sleep less well in a novel environment, or in rooms that are too hot, cold, noisy or uncomfortable. When we wake up more frequently during the night, we are more likely to remember our dreams. This gives us the impression that we dream more in certain places than others.
What’s the neurological difference between anaesthesia and sleep?
Asked by: Sophia Wan, Croydon
If a neuroscientist used electroencephalography (EEG) to record your brain’s electrical activity while you were under anaesthesia, the results would look different from how they appear when you are sleeping. In fact, your brain waves under anaesthesia would more closely resemble those seen were you to have the terrible misfortune of falling into a coma after brain illness or injury. Doctors often tell surgery patients that they will be ‘put to sleep’ during the operation, but in terms of the neurological effects of the anaesthesia, it would be more accurate (and more unsettling) to tell them that they will be put into a reversible coma.
Do dogs have dreams?
Asked by: Hannah May Lathan, Oxford
Yes. In 2001, researchers at MIT monitored brain activity in rats as they solved a maze. They found that the animals showed the same brain activity patterns during sleep. The match was so close that the researchers could tell which part of the maze the rat was dreaming about. Cats and mice show similar results, so it is likely that visual dreams are common to all mammals, including dogs.
Does warm milk help you sleep?
Asked by: Thomas Mitchell, Chelmsford
Warm milk may be soothing, but the jury is out on its soporific qualities. Milk contains a protein called alpha-lactalbumin, a source of the amino acid tryptophan. This forms serotonin, a neurotransmitter that helps to regulate mood and sleep. Consuming alpha-lactalbumin increases blood levels of tryptophan.
However, research shows that a large dose is required to give enough tryptophan for the desired effect. Milk also contains a bioactive peptide, casein hydrolysate, which is thought to have anti-stress properties, while magnesium could help with restless legs. A Dutch trial on 15 women with insomnia suggests that milk may improve sleep, especially when enriched with magnesium and the protein casein hydrolysate.
Why do our eyes move when we sleep?
Asked by: Elena Holden, London
Our sleep can be split into two main stages – rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. It is during REM sleep that our eyes dart about. This is also the stage of sleep during which we are most likely to dream. The movement of our eyes is due to specific brain activity that is characteristic of this stage of sleep.
Research suggests that eye movements may allow us to change scenes while we are dreaming. Scientists found that the neuronal activity following eye movements during REM sleep resembled that seen when people are shown or asked to remember an image when they are awake.
Do fish sleep?
Asked by: Malgo Chrzan, London
It’s hard to say if fish sleep like we do. Most can’t close their eyes and have no neocortex, which is the part of the mammalian brain that displays distinct patterns of activity during sleep. Even so, many fish settle down for the night on the seabed.
Parrotfish sleep inside a mucous bubble, perhaps so predators can’t smell them. At night, zebrafish float in the water column and are difficult to rouse. Some fish never seem to sleep, including blind cave fish and fish swimming in shoals through featureless water. It could be they receive limited sensory input and their brains don’t need to rest.
Why does reading make you sleepy?
Asked by: Sachin Shaw, Birmingham
Typically when we’re reading, we do it in a comfortable position – sitting or lying down – in a quiet place, and often at the end of the day or after more energetic activities, all of which contributes to a state of relaxation and sleepiness.
Also, an absorbing text will take your focus away from the outside world and from anxieties that might otherwise keep us alert, such as worries about tomorrow’s exam or dentist appointment. Alternatively, if you find what you’re reading boring, the effort to keep going can be tiring, in which case you’ll likely begin to daydream, which can also bring sleep closer.
Why do people dream?
Asked by: Thomas Furness, London
People with damage to the brain’s parietal lobe, which integrates sensory information, don’t dream. One hypothesis suggests that while we sleep, the parietal lobe continues generating signals, and our forebrain tries to make a story out of this activity. Other researchers have suggested that dreams occur when short-term memories are encoded and moved to long-term memory, or when unwanted connections are removed from memory.
Evolutionary psychologists contend that dreams have a specific survival value. We mostly dream about threats or stressful situations. This may be so we can safely rehearse strategies for dealing with them.
Why does the smell of lavender help you sleep?
Asked by: Liz Hayes, Lutterworth
It’s not just because it reminds you of the comforting smell of your granny’s house. Lavender oil is mainly linalyl acetate and linalool, which are chemicals that are both rapidly absorbed into the bloodstream. Studies on mice have shown that these compounds inhibit several neurotransmitters and have a sedative and pain-relieving effect. In humans, lavender also lowers the heart rate and reduces anxiety.
What causes recurring nightmares?
Asked by: Louise Carr, Exeter
Approximately 2 to 5 per cent of the population suffers from recurring nightmares, and often the reason is that they have survived some kind of life-threatening situation, such as a car accident or a violent attack. Indeed, one study estimated that between 50 to 70 per cent of patients with post-traumatic stress disorder (PTSD) experience chronic nightmares.
Other psychiatric conditions associated with an increased risk of experiencing frequent nightmares include schizophrenia, anxiety, and alcohol and drug abuse. Among people without a psychiatric diagnosis, a dream diary study from 2003 found that nightmares were experienced more often at times of stress.
Why do we talk in our sleep?
Asked by: Catherine Flind, Cirencester
When we are sleeping, there is a brain mechanism that stops the neural activity associated with dreaming from triggering speech or body movements. But this system isn’t perfect, and sometimes signals can get through. This can lead to mumbling and groaning and sometimes even proper speech (and sleep walking).
The content of sleep talking can be complex and is usually grammatically correct. It may be influenced by recent events in the sleeper’s life, but can be strange and nonsensical. Sleep talking is usually benign, although stress and other psychological problems can increase the likelihood of it occurring.
Do insects sleep?
Asked by: Caitlin Hall, Southampton
Yes. They don’t have eyelids, so they don’t close their eyes like we do. Cockroaches, however, will fold down their antennae when they sleep, which has the similar purpose of protecting delicate sensory organs. When asleep, insects aren’t just resting – sleeping praying mantises will droop downwards and sleeping bees are harder to startle than those that are having a rest.
Laboratory experiments have shown that fruit flies that are forced to stay awake are slower at learning their way round simple mazes than fruit flies that are allowed sufficient sleep.
Can you have a heart attack in your sleep?
Asked by: Clive Daniel, by email
A 2012 study at Case Western Reserve University in Cleveland identified a protein called KLF15 that is involved in regulating the electrical impulses that synchronise your heartbeat. The lowest levels of this protein in the blood occur between 6am and 10am, and this is the most common time of day for the kind of sudden heart attack caused by heart arrhythmia. This is also the time of day when you are most likely to be having vivid dreams, but it’s more likely that the stress of the heart attack would give you the nightmare rather than the other way around.
What is worse for your mood – interrupted sleep or shortened sleep?
Asked by: Susie Rees, Lamberhurst
Interrupted sleep. At least, that’s what one recent study shows. We’ve long known that sleep deprivation makes people bad-tempered and miserable, and that insomnia is linked to depression, but exactly why is less certain.
When volunteers slept in a lab and reported their mood every day, some were made to go to bed later than usual while others had their sleep interrupted several times. Both groups had the same total amount of sleep but the interrupted sleepers reported worse changes in mood. The researchers concluded that a lack of slow-wave sleep, which is the deepest type of sleep, was to blame.
But don’t jump to conclusions. These interruptions may be like being woken by a crying baby or a snoring partner. They break into your sleep cycle unpredictably at random times, therefore disrupting the normal sleep pattern. But if you regularly wake up yourself in the night you are probably waking at the end of each cycle and this would not have the same detrimental effect on your slow-wave sleep.
Why does time go so fast when you’re asleep?
Asked by: Pearl Goodwin, Lewes
Does it? Generally this is not true, and most people are good at judging how many hours they’ve slept. Some can even tell themselves to wake up at a specific time and do so. Time perception can be distorted, though, and experiments show that estimates are generally good, but people tend to overestimate time passed during the early hours of sleep and underestimate during the later hours. Time estimations during dreaming are much more variable and some people claim to have dreamt a whole lifetime in one dream.
However, the best experiments to test this come from those very rare people who can induce lucid dreams (knowing they are dreaming) at will, and then signal to experimenters to indicate what they are doing in the dream. When asked to count to 100 while dreaming or while awake, the times taken match closely. And when asked to estimate how long a dream event took, those estimates are accurate. So if time does go fast when you are asleep, you are unusual!
Why do we stretch when we wake up?
Asked by: Solang Uk, Switzerland
When you sleep, your muscles lose tone and fluid tends to pool along your back. Stretching helps to massage fluid gently back into the normal position. Also, your muscles protect themselves from over-extension by inhibiting the nerve impulses as they approach their limit.
Over time, this safety mechanism becomes increasingly restrictive. Stretching briefly takes your muscles outside their normal range. This recalibrates the feedback mechanisms that determine their normal amount of motion.
How many animals can sleep standing up?
To pull off this trick, you need legs that can be aligned vertically, so you don’t need to use muscular effort to keep them in place. You also need knees that ‘lock’ in place. Sleeping upright is advantageous for large animals because they would be slow to lumber to their feet if attacked. For smaller animals the reduction in leg springiness outweighs this benefit.
Horses, zebras and elephants sleep standing up. Cows can too, but mostly choose to lie down. Some birds also sleep standing up. Flamingos live on caustic salt flats, where there’s nowhere they can sit down. Many birds roost in trees at night using an arrangement of their leg tendons that causes their body weight to pull the claw shut around the branch. Whether this counts as standing up is a matter of semantics.
Why can some people sleep through anything?
Because they sleep more deeply and have more of the bursts of brain activity known as sleep spindles. Everyone’s sleep differs, even though we all pass through the same four stages of non-REM sleep and several periods of REM (rapid eye movement) sleep every night. In the waking brain, a large area called the thalamus acts as a way-station for sounds, sights and other stimuli coming in, but during sleep it helps suppress them.
Patterns called sleep spindles, that can be seen using an electro-encephalogram, reveal the start of non-REM sleep. Recent research has found that really deep sleepers – those who will ‘sleep through anything’ – have more sleep spindles than the rest of us. Whether you can increase your sleep spindles is still unknown.
Why are yawns infectious?
Only humans, chimpanzees and dogs have been seen to yawn contagiously. That is, they yawn when someone else yawns first. This contagion is not imitation or copying, but an automatic response to yawn when you see, hear or even think about someone else yawning.
Among the theories are that contagious yawning keeps groups of people in the same state and ready to work together. So if one is sleepy others will feel sleepy too and the whole group can coordinate their routines. Others suggest that it maintains group vigilance, keeping groups alert together. Yawning can occur in response to anxiety so another theory is that contagious yawning is used to warn others of danger.
These group theories gain some support from evidence of a brain connection between empathy and contagious yawning, but really there is no generally accepted theory to explain it.
Why do we have nightmares when we have a fever?
Temperature affects the way your brain works, and fever can produce waking hallucinations and vivid imagery as well as nightmares. Some people find that too much spicy food leads to nightmares, and this may also be because it raises body temperature. Our temperature varies throughout the day, and is especially low just before the onset of sleep. Then, during REM (rapid-eye-movement) sleep when most dreams occur, temperature control is very poor. So having a fever can lead to a much higher temperature than normal during REM sleep, and it is this that causes the over-activity manifested in our minds as vivid and scary dreams.
Why do you twitch as you fall asleep?
Twitching is a type of ‘myoclonic jerk’, an involuntary spasm in which some of your muscles quickly contract and relax again. It’s also called a ‘sleep start’, ‘hypnic jerk’, or ‘hypnagogic jerk’ and occurs during the interesting transitional state between waking and sleeping, when all sorts of odd experiences can occur.
The jerks are sometimes associated with dreams of flying or falling and some people report twitching as they hit the ground in a falling dream. Others report out-of-body experiences on the verge of sleep, abruptly ended with a sleep jerk.
Does cheese give you nightmares?
There is nothing particular about cheese, but if you go to bed with a full stomach, you may spend more of the night in REM (rapid eye movement) sleep, which is when your most vivid dreams occur. Whether those dreams are good or bad will depend on your underlying anxiety level and whether you get tangled up in the blankets.
Can you 'bank' sleep in advance?
Asked by: Clare Hastings, by email
To a limited extent, yes. A 1991 study at Wright State University in Dayton, Ohio found that after an ordinary night's sleep, subjects could take an extra nap in the afternoon and then work through the night with greater alertness that a control group who didn't nap. The study also found that performance was proportional to the length of the nap – but the effect doesn't last.
After a second consecutive night without sleep, all of the subjects performed equally badly, regardless of how much sleep they had initially. It may be that all of us are normally slightly sleep-deprived and one really good night's sleep will bring us back up to 100 per cent, but that the 'tank' isn't big enough to buffer us against more than one all-nighter.
Why do we rub our eyes when we're tired?
Asked by: Matthew Cahill, Liverpool
Tired eyes get dry, and rubbing stimulates the lacrimal glands to produce more fluid. Tiredness also closes your eyes, so you may rub to keep them open. Finally, there’s a connection between the muscles that move your eyes around and your heart. When these muscles are stimulated, a reflex slows the heart. This might be relaxing if you feel very tired.
Do people in a coma dream?
Asked by: Lucie Coltman, via Twitter
Patients in a coma appear unconscious. They do not respond to touch, sound or pain, and cannot be awakened. Their brains often show no signs of the normal sleep-wakefulness cycle, which means they are unlikely to be dreaming. Yet many people who have recovered from comas report dreams into which something of the outside world penetrated. Others recall nightmares that seemed to go on and on.
Whether they dream or not probably depends on the cause of the coma. If the visual cortex is badly damaged, visual dreams will be lost; if the auditory cortex is destroyed, then they will be unable to hear dreamed voices. If the cause is damage to brain areas such as the reticular activating system, which controls the sleep-wakefulness cycle, normal dreams cannot occur but other dream-like states might. The term ‘coma’ covers many conditions. Until we understand them better, it is hard to say which ones can include dreams.
Can you sneeze in your sleep?
Asked by: Seonaid Johnston, Perth
Even if an insect crawled across your nose,you probably wouldn’t sneeze while dreaming. During REM sleep (the phase where dreams take place), your muscles are paralysed so that you don’t thrash around and hurt yourself. This paralysis extends to reflex muscle contractions, so you can’t sneeze while you are dreaming. In non-REM sleep your muscles are free to move again but the trigeminal motor neurones responsible for triggering a sneeze are still suppressed. It is just about possible to sneeze during this non-REM sleep, but the exertion will normally wake you up.
How is lucid dreaming possible?
Asked by: James Slatter, by email
A lucid dream is when you know, at the time, that you’re dreaming. The sensation is like ‘waking up’ in your sleep. You seem more alert, logical and self-aware and can even take control of the dream. Some lucid dreamers choose to fly, others seek out a sexy dream partner and a rare few use the opportunity to meditate.
I don’t know why lucid dreaming should seem impossible but it is becoming clearer how it works. Experiments, though difficult, can be done with expert lucid dreamers who can signal to an experimenter using eye movements. Their lucid dreams most often occur towards morning, at the end of a period of REM sleep and when the brain is more than usually active. Recent brain scans show the most active areas to include parts of the prefrontal cortex and the temporoparietal junction where internal and sensory information come together to form our body schema and self image. This is probably why I feel more awake and ‘myself’ when I realise I’m dreaming.
What happens when we dream?
Asked by: Tasha Henson, Norwich
The whole brain is active during dreams, from the brain stem to the cortex. Most dreams occur during REM (rapid eye movement) sleep. This is part of the sleep-wake cycle and is controlled by the reticular activating system whose circuits run from the brain stem through the thalamus to the cortex. The limbic system in the mid-brain deals with emotions in both waking and dreaming and includes the amygdala, which is mostly associated with fear and is especially active during dreams.
The cortex is responsible for the content of dreams, including the monsters we flee from, the people we meet, or the experience of flying. Since we are highly visual animals the visual cortex, right at the back of the brain, is especially active, but so are many other parts of the cortex. Least active are some parts of the frontal lobes, and this may explain why we can be so uncritical during dreams, accepting the crazy events as though they are real – until we wake up.
Is it good to lie-in on weekends?
Asked by: Kathryn Friel, Cambridge
Some studies suggest that people who sleep more than nine hours have an increased chance of suffering illness or accident. But it isn’t clear whether this is caused by too much sleep, or if it’s simply that people predisposed to become ill are also more likely to spend longer in bed – for example because they are depressed.
In any case, this is for people that routinely oversleep. Catching up on lost sleep at the weekend doesn’t do you any harm by itself, but it may not be enough to repair damage caused by inadequate sleep during the week. A 2013 study at Pennsylvania State University College of Medicine found that catching up on lost sleep reduced the levels of stress hormones in their blood. But it didn’t improve their performance in tests that measured concentration.
Do more men snore than women?
Asked by: Miranda Calder, Windsor
Yes, about twice as many. Snoring is sometimes caused by obstruction of the nose or by excessive growth of adenoid tissue, but some is a consequence of the fact that we humans can speak.
When language evolved our voice boxes had to drop lower in the neck, creating a space behind the tongue called the oropharynx. The tongue, like other muscles, relaxes during sleep and it can then fall into this space, especially if we lie on our back, obstructing breathing or causing snoring. This space is larger in men than women, which may explain why men tend to snore while women are more likely to wake up. The result is that the men stay asleep and keep snoring... while we poor women lie awake and have to endure the noise.
Why do we get jetlag?
It’s partly because of time differences. If I fly from London to Tokyo, taking off at 6pm, I will arrive around 6am the following day by my watch. But the local time is 2pm (3pm during British Summer Time). If I try to follow the local schedule, I should go to have lunch instead of breakfast and go to bed when my body thinks it’s only the afternoon. Alternatively, if I stick to the rhythm of my body clock, I will end up trying to stay up until around 7am and then sleep through the bright, noisy day.
But time differences are only part of the story. That flight took 12 hours, and even flying business class, most of us don’t eat, sleep or relax terribly well cooped up on a plane. Long-haul flights not only maximise the time difference, they also ensure that we arrive tired to begin with.
Why don’t humans hibernate?
Asked by: Harry Tanner, Hampshire
Hibernation is a response to cold weather and reduced food availability. Most animals that hibernate are quite small and, as the weather gets colder, they reach the point where they simply can’t eat enough food to sustain their body temperature.
Humans don’t hibernate for two reasons. Firstly, our evolutionary ancestors were tropical animals with no history of hibernating: humans have only migrated into temperate and sub-arctic latitudes in the last hundred thousand years or so. That’s not quite long enough to evolve all the metabolic adaptations we would need to be able to hibernate.
Much more importantly though, we discovered fire, clothes, shelter, hunting and agriculture, all of which are much more effective ways of surviving the cold. Any ancient tribes that tried to sleep their way through the winter would quickly have been ousted by the guys with the fur clothes sitting around the camp fire in the next cave along.
Can too much sleep have negative effects on the body?
Asked by: Chris Toyne, Amersham
Studies have shown that people sleeping more than nine hours a night, are at greater risk of diabetes and obesity. But it is important to realise that the oversleeping is probably just a symptom of something else – depression being the most frequently cited. If you’re otherwise fit and healthy, it’s hard to make yourself sleep longer than you need.
Do whales sleep?
Asked by: Steven A Collins, by email
Whales, dolphins and porpoises need to retain conscious brain activity in order to take a breath because they must be able to tell that their blowhole is at the surface. To get around this, they only sleep with one hemisphere of the brain at a time. This resting state is more like a very light nap and the whale can still swim at the same time.
How can different people survive on different amounts of sleep?
There’s a difference between how much sleep people need and how much they get. Most research indicates that adults show the lowest average mortality rates with about seven hours of sleep. Life expectancy drops if you go more than two hours either side of this.
But if you have a busy life, sleep is often the first part of your schedule to get cut, so people who survive on just four or five hours may be doing just that – surviving, rather than thriving (Prime Ministers, like Margaret Thatcher and Gordon Brown are famed for getting by on just a couple of hours a night).
At the other end of the scale, some people don’t sleep very restfully. Stress, a bad bedtime routine or an uncomfortable bed can also mean you need more hours in bed to get the same amount of rest.
Why do we get more emotional when we’re tired?
Because our brains lose their capacity for balance and control. In a healthy brain after plenty of sleep, the evolutionarily older parts of the brain are controlled by various parts of the neocortex (the outer convoluted part of the brain that is especially large in humans). These older parts are similar in many other animals and include circuits specialised for emotional behaviour, including the amygdala. This responds when people look at emotional stimuli, and brain scans show a 60 per cent increase in reactivity when people are sleep deprived. Adolescents frequently get insufficient sleep and this contributes to emotional and behavioural difficulties.
Why is rail and air travel so tiring when you aren’t doing anything?
Packing until late the night before, setting off early, getting to the airport and carrying luggage, dealing with security and customs, maintaining a cramped posture for a long time, breathing low-oxygen recycled air and interrupting normal sleep and eating patterns… These are all excellent sources of physical exhaustion. Nevertheless, the real reason we feel tired when we travel is not physical, but mental.
Travelling is boring; it involves long periods of waiting for things to happen, there is limited mental stimulation and we mentally classify it as ‘the bit before the fun starts’. On a fly-drive holiday, the driving when you get there never feels as tiring because you are ‘on holiday’. New sights, smells and experiences are constantly engaging your attention and you are no longer waiting for something to begin.
Why do alcoholic drinks give me vivid dreams?
Asked by: Steven Druskovich, by email
Many people use alcohol to help them sleep. During the first part of the night it increases non-REM sleep (including deep sleep) and suppresses REM sleep (when most dreams occur).
But as the blood alcohol level drops, the reverse happens: sleep is shallower and waking more frequent, which means more dream recall, and more REM sleep, leading to vivid dreams and nightmares. This poor sleep can then make you tired and want to repeat the drinking the next night.
Why do I always feel tired after lunch?
A full stomach diverts blood to the vessels in the abdomen, to help supply oxygen to the digestive organs and transport absorbed nutrients away. This reduces blood flow to the brain and makes you feel sleepy. It's possible that this also represents an adaptation to discourage strenuous activity after a big meal. A heavy meal makes you a slower runner and sleeping it off on the prehistoric sofa was probably a safer strategy for our ancestors.
Do ants ever sleep?
Asked by: Paul Bachelor, by email
Ants definitely rest - in any given colony there will always be some individuals that are standing still, not doing anything. Ants are also inactive in cold temperatures and many species hibernate through the winter.
Resting ants exhibit loss of muscle tone and reduced sensitivity to stimuli. But they don't have a complex enough nervous system to exhibit the different brain wave patterns seen in humans during sleep; nor do they dream.
Can a smell wake you up?
Asked by: Keith Stephenson, Walsall
Smelling salts (ammonium carbonate) have been used since at least the 17th century to revive a patient from a faint. They work because the ammonia gas irritates the lungs and triggers an inhalation reflex, which alters the breathing patterns and elevates blood oxygen levels. With ordinary sleep, it is quite possible to be woken by the smell of coffee or frying bacon, which stimulates the appetite and raises arousal levels.
Together with Goldsmiths, University of London, BBC Focus is conducting its very first piece of research to find out more about two sleep phenomena: exploding head syndrome and sleep paralysis. To discover more click here or to here to take part.