Sleep is recognized as the best way to relieve fatigue. However, have you ever been in a situation where you have slept for 8 hours and still feel sleepy?Or, after only 5 hours of sleep, you can feel refreshed. In fact, it is all related to the sleep cycle.
The sleep cycle is a waveform diagram drawn by scientists and psychologists by observing the changes in the body's brain waves and various physiological function indicators during sleep. Each sleep cycle consists of sequential sleep phases ranging from 60 to 120 minutes (90 minutes on average). In an adult's 6-8 hours of sleep, there are an average of 4-6 sleep phases. 
Sleep continuity is essential for sleep quality. In different sleep cycles, there are different stages of light sleep, moderate sleep, and deep sleep. If you continue to sleep after being awakened at any time, you will not be able to return to the interrupted sleep phase, but will start again from the original sleep onset. Therefore, if sleep is frequently interrupted during the night, the patient's normal sleep pattern will be disrupted, and deep sleep and fast-wave sleep will not be obtained, and the quality of sleep will be greatly reduced. That's why sometimes even if you get enough sleep for 8 hours, you can't get rid of the sleepiness.