Light, deep, REM... sleep is complex. It can be broken down into several cycles of around 90 minutes, repeated 3 to 6 times a night. Each cycle is itself made up of alternating slow-wave and REM sleep, each characterized by different brain activity. Deep, slow-wave sleep occurs at the start of the night, and corresponds to the most restorative phase, essential for physical and mental recovery. REM sleep occurs at the end of the night, and is characterized by intense cerebral activity: this is when we dream. It plays an important role in memory consolidation. Sleep rhythms are never set in stone, but vary during the course of a single night and over the course of a lifetime. It's important to respect our natural cycles at every stage of life: going to bed at the first signs of fatigue, and getting enough sleep to meet our physiological needs.

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For further information, we recommend that you consult :

- INSERM website
- Morphée network website (health network dedicated to the management of chronic sleep disorders)