Most people have a vague understanding that rest is good for them. They know they should sleep more, slow down occasionally, and find ways to decompress. What very few people understand is what the body is actually doing during genuine rest: the specific biological processes that are only possible when the nervous system moves out of alert mode and into something far more restorative.

There is a timing system embedded in nearly every cell of your body. It runs continuously, even when you are not aware of it. It coordinates when hormones are released, when your core temperature peaks and drops, when your liver performs its most intensive metabolic work, when your immune system deploys its strongest defenses, and when your brain consolidates the memories of the day.