... the only way I could find to survive my childhood was to disassociate. To withdraw deep within myself, become as much of an empty shell as I could.

Same here. In my case, not so much withdrawing into myself as going somewhere where neither I nor my world were, so I could block out any awareness of the Hell I was in 24/7. In class, I would read ahead in textbooks, because I couldn't get in trouble for having a textbook open, and reading something, anything at least occupied my mind enough to block out the "real world" and distract me from the pain.

I notice that this sort of dissociation has become my normal way of life. I don't know if it's because my life is still pretty painful, 50 years later, or if it has just become a habit, something I reflexively jump to whenever I feel any discomfort or frustration.

boy could I use a break from being me . . .

I hear ya, sister.