When you go to sleep at night, you experience four stages of sleep. To feel the most well rested, generally, you need to wake up at the end of the sleep cycle.  

Stage 1:

The eyes are closed during Stage 1 sleep and you can be awakened without difficulty, however, if aroused from this stage of sleep, you may feel as if you havenʼt slept. Stage 1 may last for five to 10 minutes. During this time, you may feel like youʼre falling, which may cause you to jump suddenly, (called hypnic myoclonia).

Stage 2:

During this light period of sleep the heart rate slows and the body temperature decreases. At this point, the body prepares to enter deep sleep.

Stages 3 and 4:

These are deep sleep stages, with stage 4 being more intense than Stage 3. This is when REM sleep occurs. These stages are known as slow-wave, or delta, sleep. If aroused from sleep during these stages, a person may feel disoriented for a few minutes.

Typically, Rapid Eye Movement (REM) sleep occurs 90 minutes after you fall asleep. The first period of REM usually lasts 10 minutes, with each recurring REM stage lengthening, and the final one may last up to an hour. Polysomnograms show brainwave patterns in REM to be similar to that recorded during wakefulness. In the REM stage, heart rate and respiration speed up and become erratic, and the eyes move rapidly in different directions.

You are most likely to have powerful dreams during REM sleep as a result of heightened brain activity. Interestingly, paralysis occurs simultaneously in the major voluntary muscle groups.

Infants and young children tend to have the highest percentage of REM sleep, and as we age, the percentage of REM sleep declines. Infants can spend up to 50% of their sleep in the REM stage of sleep, whereas adults spend only about 20% in REM.

This article was taken from The Better Sleep Council.