After a good week or two of thinking about this little revelation I realize this was my defense mechanism. All this time I thought my main way of "dealing" with stuff was to intellectualize and rationalize. That is to say I would overthink and overanalyze things, which allowed me to step back from painful or uncomfortable stuff and deal with it in a less threatening way. But no, my main way of dealing with bad, uncomfortable, painful, or boring situations was just to not be there. The more I think about it, the more I realize huge chunks of my life aren't something I can easily remember, if I remember them at all. Thanks to all the crap I went through in junior high and high school I learned to just send my mind elsewhere until I got back to doing something I liked (or stopped feeling something I didn't like).
This is all very important to me because one of the hallmarks of good therapy is the ability to be present, which is to say the ability to be there in the moment with the person. It's also important to me because now I know why I'm denser than most heavy metals; it's because over a decade ago I made a conscious decision to not feel things, and the way I went about not feeling things resulted in me not being there. It's hard to notice stuff when you're not there. Likewise, it's hard to notice little things about what a person says or does if your mind is off somewhere else.
I call it Blissful Dissociation. It's my own little take on blissful ignorance; that which you are unaware of cannot hurt you. In my case, I was aware of it, but I consciously chose not to be present with it, which let me fool myself into thinking I wasn't there and thus not experiencing it. A kind of sick take on "mind over matter".
Now I have to stop it. You'd be surprised how friggin' hard it is to constantly stay "in the moment", how very easy it is for me to just drift off into what happened yesterday, or what will happen later today, or just some weird random creation of my mind. It's how I got through so much unpleasant stuff, whether it's from the long and boring drive up to Vegas I'm doing in a few days, to the pain of having to re-make new friends at new schools three times in one school year (or the loss of hearing your best friend hung himself).
But at least now I know, and I know how to stop it.