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Definition of Deep Sleep

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Updated February 18, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Definition: State of sleep from which it is difficult to awaken. It is represented by slower brain waves called delta activity on EEG. It is a type of NREM sleep and is called stage 3 on sleep studies.
Also Known As: Delta Sleep, Slow-Wave Sleep
Examples:
When my son is in deep sleep, he is nearly impossible to awaken.
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