While many of us think of sleep as a stretch of time where nothing happens, sleep is actually, at least neurologically. Although the importance of sleep cannot be disputed, scientists do not know exactly why so important to our survival. A rested body is much stronger and can defend itself better against infections and colds. Chronic sleep deprivation can lead to long-term mood disorders, such as depression and anxiety. Scientists have found that people who usually sleep less than 5 hours a night have a increased risk of developing diabetes. Lack of deep sleep changes the way the bodyproduces glucose. Increases sexual appetite and decreases the risk of heart disease. Lack of sleep for long periods of time is associated with an increased level of blood pressure, rhythm increased heart rate and higher levels of certain chemicals that increase the risk of inflammation. Considering literature data indicating psychophysiological variations during and due to sleep, the studying methods for this experiment are: 1. Surveys and psychological tests. 2. Polysomnography. 3. Hormone levels lab results. A survey concludes that people who sleep less of 6 hours a night, or sleeping more than 9 hours, had a 30% higher death rate than those who usually sleep 7 - 8 hours. Even those who slept less than 6 hours and generally did not had health problems but had a 1.8 times higher death rate than those who slept "normal" hours. In January 2017, a study was made public according to which insufficient sleep exposes the body to diseases by weakening the immune system. The immune system works best when has enough sleep. Seven or more hours of rest are recommended for o optimal health. Adolescents, in March 2016, showed that one in ten children are at risk of breathing disorders in sleep time. 9.6% of children in Romania are at risk for breathing disorders during sleep, of which the most severe form is obstructive sleep apnea. Children who are at risk for this problem can have signs during the night or during the day. Humans have an internal circadian rhythm, a routine and behavioral processes that occur approximately every day for 24 hours. Despite this fact, what is the right time for a person to sleep, we know which one is the best and healthier type of sleep for a person's overall health.