deep sleep

physiology

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

June 25, 2026

Quick Summary

Deep sleep, also known as slow-wave sleep (SWS), is the deepest stage of non-REM sleep. It is characterized by slow, high-amplitude delta brain waves, significantly reduced muscle activity, and the lowest heart rate and respiration levels. This stage is crucial for physical repair, growth, and development, as the body secretes human growth hormone during deep sleep. It also plays a vital role in memory consolidation and immune function. While dreams typically do not occur during SWS, it is considered the most restorative phase of sleep, making it the hardest to wake from.123

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

6 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

sleep
Light and deep sleep
Which of the various NREM stages is light sleep and which is deep sleep? The criteria used to establish sleep depth are the same as those used to distinguish sleep from wakefulness. In terms of motor behaviour, motility decreases (depth increases) from stages…
Read More
Which of the various NREM stages is light sleep and which is deep sleep? The criteria used to establish sleep depth are the same as those used to distinguish sleep from wakefulness. In terms of motor behaviour, motility decreases (depth increases) from stages…
Read More