Your sleep is divided in three main states : NREM sleep, REM sleep, and Wake. Here’s a description of NREM and REM sleep.
NREM sleep was divided into four stages in the Rechtschaffen and Kales (R&K) standardization of 1968. That has been reduced to three in the 2007 update by The American Academy of Sleep Medicine (AASM).
- N1 sleep 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. During this stage, many people experience sudden muscle contractions preceded by a sensation of falling. Stage 1 occurs mostly in the beginning of sleep, with slow eye movement. This state is sometimes referred to as relaxed wakefulness. Alpha waves disappear and the theta wave appears. People aroused from this stage often believe that they have been fully awake.
- In N2 sleep , eye movement stops and brain waves become slower with only an occasional burst of rapid brain waves. The body begins to prepare for deep sleep, as the body temperature begins to drop and the heart rates slows. EEG recordings tend to show characteristic "sleep spindles", which are short bursts of high frequency brain activity and "K-complexes" during this stage.
- The N3 sleep phase is associated with deep sleep. Delta waves appear and the muscles are more relaxed. The activity of the smooth muscles of the digestive tract increases. It is usually during this deep sleep that enuresis or somnambulism may appear. Deep sleep occurs for the first time usually 30 to 45 minutes after falling asleep. Learn more about N3 stage.
During REM (rapid eye movement) sleep, brain waves mimic activity during the waking state. The eyes remain closed but move rapidly from side-to-side, perhaps related to the intense dream and brain activity that occurs during this stage. Here’s a recap of different stages of sleep: