I've taught myself to dissociate. When I first started meditating, I'd start dissociating instead, and at the time, I didn't complain, actually welcomed it because I was actively going through a lot and it was an escape.

Now, I realize when I dissociate...almost instantly. The anxiety, tension, pain that I feel instantly vanish and the numbness takes over, but for the most part right now, I'm not actively choosing to do it. It just "happens" when the tension becomes too much, even though, to me, I've felt worse and if I don't "feel" it, how can I work on controlling it? I have to realize it's going to happen before it does and work on other techniques. The imagery idea is a good one.