When we've been awake for a long time, our sleep drive kicks in and tells us we need to sleep. During REM sleep, the cortex – responsible for cognition and emotion-processing – is activated in some regions and deactivated in others. After cycling through non-REM and REM sleep around 4 to 5 times, the basal forebrain and other structures receive signals to start exiting sleep. WHEN SLEEP GOES WRONGIn the U.S. alone, 50 to 70 million people experience some type of chronic sleep disorder, according to the American Academy of Sleep Medicine (AASM). In the United States, a list of board-certified sleep medicine physicians and accredited sleep disorders centers is available from the American Academy of Sleep Medicine.

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