Throughout the night, “We’re going in and out of this rhythmic, symphonic pattern of the various stages of sleep: non-REM 1, 2, 3 and REM,” said Rebecca Robbins, an instructor in medicine at Harvard Medical School and an associate scientist in the division of sleep and circadian disorders at Brigham and Women’s Hospital:
The Four Stages Of Sleep
non-REM 1
non-REM 2
Deep Sleep (non-REM 3)
REM sleep
Repeat every 90-110 mins. 4-6x
As you doze off, you enter the first stage of non-REM. This lasts less than 10 minutes and is considered a light sleep.
Your breathing and heart rate decelerate and your muscles relax as you slip into the second stage of non-REM sleep, where your body temperature drops and your brain waves get slower.
Then you enter the third stage, known as deep sleep, when your body repairs your bones and muscles, strengthens your immune system, releases hormones and restores your energy.
After that, REM sleep begins, and your heart rate, breathing and brain activity all increase. Brain regions involved in processing emotions and sensory input (from your dream world) light up. Meanwhile, your brain paralyzes the muscles in your arms and legs, preventing you from acting out your dreams, Dr. Dasgupta explained.
Ideally, you move through the four stages in 90- to 110-minute cycles that repeat four to six times in a typical night. Then, after your last REM cycle, you wake up rested and alert, said Dr. Indira Gurubhagavatula, a sleep specialist at Penn Medicine and associate professor of medicine at the V. A. Medical Center in Philadelphia.
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