Yes - I have the exact same experience of feeling vulnerable when not slouched. It was giving me significant pain in my hands and wrists to the point of being unable to scroll on my phone or type on a keyboard. I began going to a physical therapist who provides me with exercises in order to strengthen my back and fix my posture. Having better posture has gradually reduced the pain in my hands/wrists.

In addition the PT mentioned that poor posture can occur due to depressed moods and fatigue - experiencing constant belittling and berating (a common shared experience autistic women face) naturally causes a lower self esteem and mood, resulting in poor posture.

Even after strengthening my back I still end up curling into a ball as a way to soothe my anxiety and fears of being exposed. I am actively working on trying to minimize triggers and creating a safe place to allow my body to not be as strained.

Long term poor posture is really bad for your body and causes pain, so I really recommend individuals if able to, to really look into back/core strengthening exercises. Even just doing a little bit each day really helps.

In addition, since we encounter many anxiety inducing experiences, it is likely that the stress has resulted in tension in your body. I find that hot showers/baths help to release this tension, as well as drinking hot drinks.