Your nervous system is a super complex network of nerves and specialized cells that governs your movements and takes in sensory information so you can interact with your world. It's constantly transmitting messages to and from your brain.
At one point, doctors and scientists believed that we had little or no control over this system, kind of like breathing or the beat of a heart. It just functions.
But, you actually can activate the part of your nervous system that is responsible for resting and regeneration, and that is how you can prevent most chronic issues caused too much stress.