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The stages of sleep

Sleep stages 1, 2, and REM consist of light sleep, while 3 and 4 comprise deep sleep.

Stage 1

During stage 1, you drift from being awake to being asleep. This is a light, NREM sleep that doesn’t last very long. You may start to relax and dream, but may also twitch as you transition into stage 2.

Stage 2

Stage 2 of the sleep cycle is still a light sleep, but you are drifting into a steadier sleep. Your breathing and heartbeat slow down, and your muscles relax. Your body temperature decreases, and your brain waves are less active.

Stages 3 and 4

In stage 3, you enter deep sleep, and stage 4 is the deepest sleep stage. During deep sleep, your breathing, heartbeat, body temperature, and brain waves reach their lowest levels. Your muscles are extremely relaxed, and you are most difficult to rouse.

Stage 4 is known as the healing stage, when tissue growth and repair take place, important hormones are released to do their jobs, and cellular energy is restored.

REM sleep

Your first REM cycle of the night begins about 90 minutes after you fall asleep and recurs every 90 minutes. Your eyes move around quickly behind your eyelids and your brainwaves look similar to those of someone who is awake. Your breathing, heart rate, and blood pressure rise to near-waking levels.

REM sleep, often referred to as stage 5, is when you are most likely to dream.

Your arms and legs become temporarily paralyzed during this stage to prevent you from physically acting out your dreams.