I think it is a stress response. People who do not have a diagnosis like PTSD also get this, sometimes with daily vomitting and other problems, from living a high stress, no relaxation lifestyle.
I had a young, healthy student two years ago. She was juggling two small toddlers, a demanding job as a special ed paraprofessional, full time night classes at college (where I teach) a husband, and matching her shoes to her shirt in the latest fashion. She had set a goal for herself and refused to slow her progress, even though she could not eat and had constant migraines. I asked her why she didn't drop her course load, indicating that she might have a totally different (more positive) college learning experience if she felt better and could go at a more usual pace. She agreed that would be best, but was undeterred because she had a sense of shame and to mitigate it, promised herself that she would complete college by a certain date, indicating that she was already "late" being a mom and older than some of her peers.
PTSD or not, it is far simpler to view the "stress creep" from the position of listener. And advice is easy to give. But it is hard to accept our lives, hard to listen to advice, and hard to know what will really work out for the best long-term.
I am going through the tummy stuff again. It all relates to making big decisions for me. I like that Fly Away Home also mentioned decisions.
I don't feel a sense of "trust" in this world, and feel that no matter what I decide, I am still living in the land of my trauma. Every decision I make is an attempt to distance myself and my immediate family from anything negative or traumatic. Obviously, like my student, I think when there is a deep underlying negative belief, it propagates further stress.
It would be nice if a big, life-altering decision could be made on simpler terms, such that a huge knot would not form in my being and stay tied there for months on end. I'm going to try walking when the weather cooperates. It helps me cope.