What strikes me, is that even though you and your T are both trying to help disassociation, that you are DEMONSRATING that you don't feel safe enough, to associate. Body sensations are important signs to follow.
Be easy on yourself, and your therapist. It would be interesting to interview a few other therapists, and see if you relax more. Sometimes, our instinct senses a trait in the other person, that reminds us of a trauma, and we disassociate, even though we don't want to (practiced pacing at my rate and following what felt/ I demonstrated was safe and interesting. I had to drop any timeline, so did the therapist.
Maybe you might want to try a different approach at first, where you aren't alone, like in a group? Or work your way into therapy through less formal settings, like 12 step groups. There are non-verbal therapies, too. Mindfulness can be intense: it made me worse at first, but it go better
The other part of of therapy, is that we so 'project' who we are afraid of, to our therapist. But hopefully, it is comfortable enough to 'work through' (i.e. talk about what bothers you-if your are aware of it.). If it does remind you of something stressful, remind yourself that you get to practice being an equal authority in therapy, always voicing what works for you and not.
I have been in your situation, and I tried to stay with it. But my disassociation never got better, so I switched therapists. I found someone, whom I relaxed with, and I used skills to stay associated-like standing up, moving around the room, and tell the therapist what I wanted to do-even if it was being silent, so I could look around the office.
Therapy has a lot of trial an error in it, but it is always a learning situation of what works, or not. I never went back to my first therapist; it was 7 years later until I could finally sit in the room with someone, and not disassociate due to fear.
Good luck!
