To understand why we need sleep it might be best to recall what happens when people don’t get enough sleep.
Lack of sleep affects thought processes. For example, if you’re deprived of sleep and you attempt to do maths, you’ll find you do your calculations more slowly, and with a higher likelihood of errors.
Lack of sleep also affects you physically. Your coordination suffers, and you lose your ability to do things with agility. Reaction time slows down. For these reasons, driving a car is extremely dangerous, if you’ve had too little sleep.
Chronic sleep deprivation has long term health effects. Studies have shown that lack of sleep contributes to increased risk of obesity, diabetes and heart disease.
How much sleep a person needs varies by individual. It averages about 7 hours a night for adults, but can be anywhere from 5 to 11 hours. Jim Horne, from the Loughborough University’s Sleep Research Centre, has a simple answer: “The amount of sleep we require is what we need not to be sleepy in the daytime.”