I tried three types of martial arts over the years (and never got very good at them...) but do feel that I benefited a fair amount from the study. Please note that I'm not an expert, this is all from my own experience.
From my current perspective, I think I would partly dissociate during virtually all the classes; numbing and I think "derealizing", though that was a pretty normal state for me and I never stopped looking somewhat "normal" to my knowledge. I just thought that's what feeling stressed was like, I think, though I knew I found it more stressful than a lot of the other students seemed to; I connected that to the abuse, and generally didn't talk about it. However I couldn't learn to react automatically in the same way a lot of the people did, I sort of had to remind myself what I was going to do mentally. It's hard to describe, but I never really advanced much.
What I did really enjoy was doing slow movements, feeling strong doing them, and working on balance. I feel more connected to more of myself when I work on balance in a calm setting.
I also felt pretty good at feeling peoples' energy re. when they were going to attack, during sparring, I think. However I would numb out if there was too much going on, and lose that sense. I've only really connected the term "dissociation" with what I do, in the past year, however, in spite of therapy for 25-odd years. (Do some therapists think it's harmful to folks to point that stuff out to us, or something? Why did I have to read about it to make the connection to that word...)
I did some hapkido in my 30s, which has some things similar to aikido. I also did karate in an all-women's dojo in my 20s. The most enjoyable for me was arnis, from the Philippines, using bamboo sticks in patterns. I don't think I numbed out when doing that, it didn't remind me of anything perhaps.
Slow, contemplative movements and working on conceptions and feelings of your own and others' energy seem to be done more in the "soft" martial arts like tai chi or aikido.
So, if you get more triggered by the "hard" martial arts (like karate) in the sense of dissociating or maybe also having other reactions, there are other options that might be less triggering but that can also allow you to work on some related issues. There are lots of martial arts, so you could try for one that benefits you rather than being so stressful that you can't progress in it or your issues.
This all seems related to the issue of exposure therapy, where folks who dissociate can't benefit from some such "therapies" because, well, we just dissociate again, so it's really more like almost a retraumatization... Probably dissociating during a martial arts class isn't going to let you learn as much, at the very least. (I kept banging my head against that wall for quite a while though.)
The "soft" martial arts are not totally useless in direct self-defense, I think, though I'm not an expert at that. The "hard" martial arts are supposed to be quicker to learn effective action with, for an actual attack. I never used any physical techniques as my martial arts work was all after my family member's direct violence toward me.
I do think it helped me feel peoples' energy better, my own, and maybe stay safer and more centered in some situations though.
