@heyjoe415 I would guess that relief of both tension and pain would help to restore Vagus nerve tone, which in turn would improve its ability to help you to relax. When under stress, including pain stress, the sympathetic system ramps up to protect you. That means increased cortisol, adrenalin, and all the attendant changes to body systems when you're preparing to flee or to fight for survival. The body doesn't really care about WHAT the stress IS, it just knows that there is a threat, perceived or real, and it needs to protect itself. It does that with increased arousal. This is accomplished with the adrenalin, and the cortisol soon follows. In a protracted state of arousal, no system is going to do well over a length of time.

So, the stress response means more blood to the extremities, pilo-erection, increased blood pressure, more sugar deposited in the blood by the liver, etc. Oh, and decreased motility in the alimentary tract since you don't really want to be digesting food while your muscles are calling for everything you have.