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. 2020 Nov 23;13:1178646920970902. doi: 10.1177/1178646920970902

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© The Author(s) 2020

This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 License (https://creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sagepub.com/en-us/nam/open-access-at-sage).

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Figure 1. — Stages of sleep. Sleep is composed of 2 phases: Rapid Eye Movement sleep (REM), and the Non-REM sleep (NREM). The NREM phase consists of 4 stages: Stage 1, which is transition from being awake to falling asleep; Stage 2, the period of light sleep during which the eyes movements stop, Stages 3 and 4, which are also called Slow Wave Sleep (SWS) (Reproduced with permission from Bernard¹⁰).