From the later stages of the fetus, people get sleep, especially after birth. If you average eight hours of sleep per person per night, then a 70-year-old spends more than 200, 000 hours sleeping. Human life is precious and limited, and it is not worth it to spend so much time on a single, cyclical, and unlearned activity. Believe everyone will ask: "why?" Since the 1950s, the understanding of sleep has been deepened by the invention and application of polysomnography. According to observation, healthy people can endure hunger for up to three weeks, but as long as don’t sleep for three days and nights, people will become restless, mood swings, loss of memory, judgment, and even some delusion and hallucination, so difficult to insist on the activities of daily life. Therefore, sleep is an absolutely necessary and indispensable life requirement for everyone.
Although sleep is so important to everyone, but different people have different needs for sleep, Generally speaking, women need more sleep than men. Some people only slept for 3 ~ 4 hours per night is sober, spirit is full, but others must sleep 10 ~ 12 hours every night, otherwise can giddy, listless, work hard during the day. Some famous people in history have been known to sleep less. Napoleon, for example, slept four hours a night, but he was also known for his good sleep. So in terms of length of sleep, everyone's requirements are different. For insomniac patients, it is better be compare with oneself not insomnia, and don't compare with others. For healthy adults, sleeping seven to nine hours a night is enough.