Asked by: Richard Powling, Martlesham
If by a ‘start’ you mean a physical twitch or jerk, then you’re probably waking from REM sleep and your paralysed muscles are suddenly coming to life rather slowly. Most dreams occur during REM sleep, and to prevent you carrying out dreamed actions the connections to the motor neurons are inhibited.
In a normal night’s sleep you’d be unaware of this paralysis; it wears off gradually before you wake. But if you wake suddenly, the muscles sometimes twitch. This is a ‘myoclonic jerk’ – an involuntary twitch that occurs in some neural diseases, but more often in healthy people when falling asleep. Some people are woken frequently by myoclonic jerks.
You’re more likely to wake with a start if you’re stressed or your sleep patterns are disturbed. You may also wake up still paralysed and be unable to move for a few seconds or even minutes. This is known as ‘sleep paralysis’ and can be very scary if you don’t know what it is.