ARTICLE
Sleep Disorders
Dr. Jonathan Deong KK
Ear, Nose & Throat surgeon
The normal sleep cycle consists of 4 stages of non-REM sleep cycles and 1 cycle of REM (Rapid Eye Movement) sleep throughout the night. When your sleep cycles are disturbed, you wake up feeling tired and difficulty concentrating during the day.
Source Link
https://blog.teleme.co/2018/10/19/sleep-disorders/