The Different Stages of Sleep

Sleep mainly consists of two major categories: non-rapid eye movement sleep (NREM) and rapid eye movement sleep (REM), which can be further divided into the following stages:

Non-rapid eye movement sleep (NREM)

Stage 1 (N1)

Characteristics: This is the lightest stage of sleep and marks the transition from wakefulness to sleep. Brain waves slow down from beta to alpha, with some theta waves appearing. Muscles begin to relax, the eyes move slowly, and you're easily awakened by minor disturbances.

Duration: Typically lasts 1–7 minutes. For example, when you're just drifting off in a quiet environment, a sudden phone ring may wake you easily.

Stage 2 (N2)

Characteristics: Brain waves feature sleep spindles and K-complexes. Muscles relax further, body temperature drops, and heart rate slows. This is still light sleep, but deeper than N1 and harder to wake from.

Duration: Accounts for about 40–50% of the total sleep cycle, usually lasting 10–25 minutes. When you briefly wake at night and recall your sleep, it's often during N2.

Stage 3 (N3)

Characteristics: Also known as slow-wave sleep (SWS), dominated by delta waves. It's the deepest stage of sleep where the body undergoes repair and recovery. Growth hormone is actively released, and it's very hard to be awakened. If woken, you'll feel disoriented.

Duration: In young people, it makes up about 20–25% of total sleep time, usually lasting 20–40 minutes. This stage shortens with age.

Rapid eye movement sleep (REM)

Characteristics: Eyes move rapidly in different directions. Brain activity becomes highly active, resembling wakefulness, with beta waves reappearing. Most body muscles are temporarily paralyzed to prevent acting out dreams. This is the main stage where vivid dreams occur.

Duration: The first REM stage begins around 90 minutes after falling asleep. It recurs several times during the night, lasting from a few minutes to over 30 minutes, gradually increasing in duration. REM accounts for about 20–25% of total sleep time.

The sleep cycle progresses from Stage 1 (N1) to Stage 2 (N2), then to Stage 3 (N3), followed by REM sleep, and then repeats. Each cycle lasts about 90–110 minutes, with 4–6 cycles per night. Maintaining this natural sleep rhythm is vital for both physical and m