It’s thought that the body does most of its restoration during what’s known as ‘deep sleep’, one of the three stages of non-REM sleep. While the heart, breath, and brain slow right down during this recovery phase, the body releases hormones to repair cells and support bone and muscle development.
It’s also when your body resets its stores of adenosine, an energy compound that builds up while you’re awake and helps you feel drowsy at the end of the day12. If you don’t get enough sleep overnight, the level of adenosine won’t go down enough and you’ll wake up feeling tired.
Adenosine isn’t the only thing being reset overnight: recent research shows that deep sleep may also flush out end-of-day toxins that could play a role in the risk of brain degeneration and disorders13.