Just checking in quickly (because it turns out I do have internet access on my holiday!) and thought I'd throw a couple of pennies in on this one.

I don't know if I so much torture myself, but I do willingly and knowingly cause myself pain (or ask for it inflicted on me) because my body responds to it with a fight or fly mechanism. I get adrenalin pumping and I generally get really sensitive to touch and my sense of hearing sharpens. Now, if there is no way to fight or fly (due to physical restraint *ahem* or just not being able to escape from it), it just seems to convert into a truckload of endorphins running a merry race around my body Which of course makes me feel good.

I used to wonder why I did those kind of things, now I just accept that I like it, and as long as it doesn't significantly or permanently harm me, who cares?