Carrie's suggestions make a lot of sense. I wanted to say something too but wasn't sure what would be helpful. I'll often be asked by somebody why I am staring at them or what I am staring at, or I've caught myself staring out the window at nothing, and in all of these cases I was not looking at anyone or anything real - I just simply wasn't there. One of the most common places where I'm likely to dissociate is at therapy. I have caught myself there digging my fingernails into my arm (without thinking about it) to bring myself back or to keep from spacing out. I guess it must be triggered by thinking about things that are more difficult to deal with. One thing that I have been trying (and I think it usually works) is to wear a lot of rings, especially when I know I'm likely to be in a situation where dissociation is likely, such as going to therapy. Fiddling with the rings gives my hands something to do and can keep me grounded. Other things that keep your hands busy, especially if they involve some kind of tactile stimulation, might also help.
<font color=purple>"The real problem of mental life is not why some people become insane, but rather why most avoid insanity." -Erich Fromm</font color=purple>