Sleep is a normal activity in most higher organisms. Every human being, on average, spends a third of his or her life sleeping. Babies and children spend more time sleeping than adults while old people sleep less. The sleep-wake cycle is controlled by an internal biological clock which usually coincides with the day-night cycle. We do not know yet what sleep does to our body except that we feel refreshed after a good night’s sleep. But what lack of sleep does to an individual is quite well known. Prolonged lack of sleep leads to irritability, lack of concentration and even hallucinations. Thus, sleep certainly has a restorative function which helps the body face another active day.