National Sleep Foundation crucial https://sleep.org/articles/what-happens-during-sleep/ body temperature naturally increases Lee, 2009 seven of dozing off There are 4 different stages in this sleep mode stages https://sleep.org/articles/what-happens-during-sleep/ National Sleep Foundation Lee, 2009 an average adult takes 5-6 REM cycles every night https://sleep.org/articles/what-happens-during-sleep/ sleep stages: What happens during sleep https://sleep.org/articles/what-happens-during-sleep/ National Sleep Foundation Lee, 2009 Lee, 2009 an average adult takes 5-6 REM cycles every night Lee, 2009 full sleep cycle https://sleep.org/articles/what-happens-during-sleep/ During deep full sleep cycle Lee, 2009 Lee, 2009 Lee, 2009 five stages of sleep sleep cycle Lee, 2009