The answer to this question would be: sleep apnea.
Sleep apnea is a condition when someone stops breathing when sleeping. This was mostly caused by blockade of the airway by the tongue. When sleeping, the tongue might go backward covering the airway. If the blockade is partial then it would be snoring. If the tongue fully blocks the airway then it causes the breathing to stop.
Sleep apnea can decrease the quality of sleep, makes someone feel tired after wake up.
