What happens when we sleep

Sleep is central to maintaining your physical and mental health, but many people don't sleep enough. We all do it, but what happens to us when we sleep? Click here to subscribe to The Economist on YouTube: Every night almost everyone on the planet enters into a state of unconsciousness and paralysis - but what is really happening inside the body when we drift off, and what's the impact if we don't get enough sleep? Sleep is regulated by your circadian rhythm, or body clock located in the brain. The body clock responds to light hews ramping up production of the hormone melatonin at night, and switching it off when it senses light. There are four stages of sleep that the body experiences in cycles throughout the night. On a good night we cycle through these stages four or five times. Stages one and two are light sleep. This is a transition from being awake to falling asleep. Heart rate and breathing begin to slow, body temperature falls,