The momenta of individual objects changes. The total momentum remains constant. I have to disagree. If you have two cars that collide head on, the momentum of both vehicles stops. The ENERGY created by the impact causes usually, some reverse momentum but the momentum is lost.
As the SNS continues to trigger physical reactions, it causes a wear-and-tear on the body. It's not so much what chronic stress does to the nervous system, but what continuous activation of the nervous system does to other bodily systems that become problematic.
What Is the Sympathetic Nervous System? While your brain, which is a vital part of the central nervous system, has the capability to control your conscious actions like walking, thinking and talking, your body also has an autonomic nervous system, which regulates your bodily functions, like the beating of your heart, your breathing, the way you digest your food, your sweating patterns, etc.