Deep sleep generally only accounts for about 1/4 of the overall sleep time, but deep sleep time is actually a period of time that is more likely to relieve fatigue. If you sleep for eight hours every night, deep sleep is generally around two hours, but these two hours do not occur consecutively, it occurs periodically, that is, from light sleep period to light sleep period, followed by medium sleep period, and finally deep sleep period, and then into rapid eye movement sleep period, followed by the next cycle. However, if you feel particularly tired after waking up the next morning and the nighttime sleep time is still okay, you need to pay attention to whether there is not enough deep sleep period, and you can go to the respiratory department or neurology department of the hospital with the condition to do polysomnography.