Usually sleepers pass through five stages: 1, 2, 3, 4 and REM (rapid eye movement) sleep.These stages progress cyclically from 1 through REM then begin again with stage 1.
This is why if you take a short nap during the day, you’re still able to fall asleep at night.
But if you take a nap long enough to fall into deep sleep, you have more difficulty falling asleep at night because you reduced your need for sleep.
In deep sleep, there is no eye movement or muscle activity.
Deep sleep reduces your sleep drive, and provides the most restorative sleep of all the sleep stages.
Most people experience three to five intervals of REM sleep each night., breathing becomes more rapid, irregular and shallow, eyes jerk rapidly and limb muscles are temporarily paralyzed.
Brain waves during this stage increase to levels experienced when a person is awake.
The different cycles of sleep last for different amounts of time during the night.
Non-REM sleep dominates the first half of the night, while the amount of time spent in REM stage sleep increases during the second half.
Stage 1 is light sleep where you drift in and out of sleep and can be awakened easily.
In this stage, the eyes move slowly and muscle activity slows.
A complete sleep cycle takes an average of 90 to 110 minutes, with each stage lasting between 5 to 15 minutes.