I think everyone can easily answer the question of why a person needs sleep. To rest, right? But in reality, everything is much more complicated than we think. “Sleep-wake” is a complex biological cycle along with thermoregulation (our body’s ability to maintain a constant temperature, unlike, for example, snakes and lizards), menstruation in women, body growth with accompanying changes in hormonal levels, heartbeat, breathing, metabolism and etc. All of the above processes are interconnected with each other and with periods of daylight. Perhaps you have heard that each of us has a “biological clock” inside of us? If you conduct an experiment and isolate a person in a dark room for several days, then he will also sleep and be awake, that is, live, obeying the laws of biological rhythms, but only the duration of his sleep will be completely different. But it is absolutely impossible not to sleep. As a rule, any sleep disorder is either an adaptation disorder due to frequent changes in time zones, or an independent disorder that entails certain physical and psychological consequences, or a symptom of some physical or mental illness. Remember that when you get the flu, you sleep more than usual, or vice versa, when you experience severe toothache, your sleep is interrupted or you cannot sleep at all. It turns out that conditions when there is not enough sleep is a sign of illness, but when there is too much sleep, this can also be a sign of a painful condition. First, let's try to figure out what exactly lack of sleep leads to. Lack of sleep causes people to get sick. It is known that lack of sleep produces less growth hormone, which is involved in the regeneration (restoration) of body tissues. Often this work is performed by the body at night, when we are resting. Due to the reduction in sleep, the recovery capabilities of our body are also reduced. Cells do not have time to renew themselves, our organs begin to work worse and the body’s resistance to disease decreases. Our immune system also fails to cope. It also consists of cells and organs. This is why we sleep so long during the flu. Our immune system works with special tension, producing antibodies to bacteria that have attacked the body. Lack of sleep makes us stupid. When we are overtired, our ability to concentrate and remember decreases. The longer we stay awake, the more distracted we become. People who don't get enough sleep study and work worse. Children, as a result of lack of sleep, often exhibit behavioral characteristics such as hyperactivity, inability to concentrate, excessive fatigue, lethargy and even aggression. Lack of sleep makes them fat. In modern research, scientists are receiving more and more evidence that chronic lack of sleep leads to metabolic disorders. Neurotransmitters (biologically active chemicals that trigger one or another chemical reaction) of our body such as insulin (regulates blood sugar levels), leptin (regulates fat metabolism, excess leptin helps suppress appetite, and deficiency contributes to obesity), ghrelin (high its concentrations signal saturation), thyroid and adrenal hormones constantly provide a level of internal energy adapted to the body's needs, at which our organs can work optimally. And during sleep, growth hormone launches a program of comprehensive renewal of the body using a large amount of energy accumulated during the day. The body receives this energy, first of all, by burning fat from its reserves in the buttocks, abdomen and thighs. And since we don’t eat while we sleep, it turns out that we lose weight overnight. Lack of sleep makes us grow old. Lack of sleep affects a person’s carbohydrate and hormonal metabolism in the same way as the normal aging process. An experiment was conducted in Chicago in 1999,!