Why do people dream? This is a question that everyone updates, because everyone dreams. Recently at an international psychology conference, Professor Shen Zheng of the School of Psychology at Peking University reported, “Dreams are part of normal human physiology; they are unconscious mental activities during sleep, and if people are deprived of the right to dream, they will have depressive symptoms.” All people dream during sleep, and dreams account for about 1/4 of sleep time. some dreams are remembered when waking up, but many dreams leave no memory. As the saying goes, there are dreams in the day and dreams in the night. In fact, the dreams in the first half of the night are mostly related to the current day or recent memories; the dreams in the second half of the night are mostly related to distant memories; the dreams before dawn are mostly borderline, with more perceptual components, which are easy to be remembered at this time. There is a great correlation between dreams and the environment of sleep: when a person sleeps, if he sprays water mist on his head, the dream will encounter heavy rain, river or ocean; if he slowly turns his calf, the dream may fall into the abyss or be chased; if he presses his hand or other objects on his forehead, he will feel afraid and chased. Why is dreaming during sleep? Because when sleeping people stop acting, the body enters a resting period, dreaming does not mean bad sleep quality. Dreaming can eliminate fatigue and recuperate the body; dreaming can organize, classify and accumulate knowledge; dreaming is also an opportunity for epiphany and innovation, and many inventions in history were invented in sleep; dreaming can also make people maintain a good state of mind and leave some worries behind during the day. The quality of sleep is related to one’s health, and dreams affect one’s energy and mood. So the right amount of appropriate dreams is a normal physiological phenomenon, if you wake up in the morning and feel that you have been dreaming all night, it means that there is a sleep disorder and you need to ask a professional doctor to look at it.