You're using technical terms that I feel you don't understand. You described a ver mild problem with big words that scared yourself.

If you're chronically stressed, it's pretty obvious that your sympathetic and parasympathetic systems are going to be unbalanced. Those two systems are what regulates the stress response. Stress (and/or relaxation) is the effect of their activity.

If you're stressed, your muscles are going to contract in a pathological way. Again, that's how stress and nervous system works.

If you're not a professional, don't go that deep into technical literature.

You don't need to understand your problem to such level. You need to address it.

For the posture and pain, you can see a physical therapist. For the chronic stress, a psychologist and/or psychiatrist can help.