REM

Sleep apnea is a serious sleep disorder that occurs when a person's cycle of breathing is interrupted during sleep. Untreated sleep apnea can disrupt the sleep cycle hundreds of times a night.

The sleep cycle means how human sleeps and at what time. For example if everyday I wake up at 7 in the morning, then take a nap at 12 at noon and go to sleep at 11 at night that is called sleep cycle.

REM or Rapid Eye Movement. You sleep in cycles, moving from lighter to deeper sleep and back. A sleep cycle lasts about 90 minutes, with REM occurring toward the end of each cycle. The REM stage gets a little longer in each cycle; you may only dream for a few seconds in the first sleep cycle, and for a large percentage of the last cycle of the night.

you will mess up your sleep cycle