The best way to understand why we sleep is to look at what happens when we don't get enough.
Missing just one nights' sleep is not fatal and simply causes irritability the next day.
If a person misses two nights sleep, the situation gets far worse. After three days, a person will start to hallucinate and clear thinking is impossible. With continued wakefulness, a person can lose grasp of reality. Rats forced to stay awake continuously will eventually die, proving that sleep is essential. Sleep deprivation has been used as a form of torture.
A person who gets just a few hours of sleep per night can experience many of the same problems over time.
Sleep is a basic function of the body, as necessary as eating or exercise. When the body doesn’t get it, things can go seriously wrong. Sleep deprivation weakens the immune system, leaving us more susceptible to diseases and disorders such as diabetes, cancer and the common cold.
It is not uncommon for people who suffer from sleep deprivation due to sleep disorders - sleep apnea, narcolepsy, insomnia, etc - to also suffer from other problems including diabetes, asthma or a second sleep disorder.
Sleep deprivation also causes stress, which weakens the immune system. Sleep deprivation and stress can upset mental processes. People may suffer confusion, memory loss, irritability or emotional highs and lows. If someone already has a mental disorder, sleep deprivation only adds to the problem.
Two other things are known to happen during sleep. Growth hormones in children are secreted during sleep, as are chemicals important to the immune system. A child's growth can be stunted by sleep deprivation.
Sleep gives the body a chance to repair muscles and other tissues, replace aging or dead cells while it gives the brain a chance to organise and archive memories. Dreams are thought by some to be part of this process.
The message is clear – make sure you get your full eight hours a night