Asked by: Maggie Jackson, Leeds
Because it is. Our emotions are bodily functions that involve our brain, nervous system and the hormones that control heart rate, breathing, digestion, sleep and much else. Brain scans show that physical and mental pain both involve the same areas, including the anterior cingulate cortex.
Humans are social creatures who have evolved to live in groups and take relationships seriously. So when a friendship turns nasty or a lover leaves us all these emotional forces come into play.
Get more fascinating Q&As from BBC Focus magazine by following @sciencefocusQA