I'm sorry you have yet to receive a reply to this post. Perhaps the right members have simply missed it. I can't answer your question. But I thought I would at least offer a thought or two and, hopefully, others more knowledgeable than I, will follow.

I don't have factitious disorder. My tendency is to avoid doctors and other medical professionals as much as possible. But I can still sort-of relate to what you described. I'm a very private person, an "urban hermit", if you will. Having waged a life-long struggle with my gender identity, among other things, I became skilled early in life at being secretive. Plus, I also have a history of self-injury which I've also done a pretty-good job of hiding. (There were a few instances where I ended up having to see a doctor. But I always seemed to come up with a rational explanation for what had occurred. On a couple of occasions, the doctor I saw even provided it!)

Anyway, During the times when I have engaged in self-abusive activity, I knew what I was doing was not healthy and could even lead to another medical appointment or even some sort of permanent injury (which in one case in particular it has.) But I was powerless to stop it kind-of going on auto-pilot as you said. I guess it would, perhaps, take a psychologist to say whether or not your experience (or mine) constitutes dissociation. It's not what I typically think of as dissociation. But, then, despite my mental-health struggles over the years, I still don't know that much about psychology. Perhaps other MSF members will have some more knowledgeable thoughts on the subject. Best wishes...