Hi, I cannot relate to having PTSD due to psychedelic experiences, but I have experienced some of the things you have mentioned such as the shivering and even my body totally shutting down during a flashback. My therapist has said some of the same things as yours that these things from our past are there, but there are ways through intense talk therapy and bringing out those emotions that we can work through them in positive ways and eventually move on. My PTSD stems from extensive abuse so it is totally different from yours, but still we both experience some of the same horrible anxieties. Just keep working hard with your therapist. I also do a daily journal which helps me a lot.