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.