Clinically we do appear to be very sleepy during the day, but very spiritual at night, there are two concepts that can be explained from a scientific point of view: 1, circadian rhythm, or what we call the biological clock, the normal time should be 3-6 am, we are the most sleepy, he will tell us when it is time to eat, when it is time to sleep, sleep well, it is time to wake up. 2, constant sleep drive, his principle is the time to be awake The longer. The more you want to sleep, especially in the growth period of children and adolescents is very obvious. In this process, there will be our circadian rhythm and constant sleep drive these two in the crossfire, there will be a sleep forbidden area, that is, in front of the normal sleep can not sleep for a period of time, often this time is the most awake moment, the human senses will be very sharp. Generally in the adult sleep forbidden zone is between 18-22 points, in this time period you can not sleep, and then may do something such as watching cell phones, watching TV, reading books, will be more and more excited to brush. By the time our circadian rhythm should sleep, this time are sleepy tend to be defeated by excitement, will lead to the biological clock is broken, will feel more awake.