I remember that, as a child, I would lie in bed with my legs and arms slightly apart from my body, and I would pretend that I was tied by every limb and was about to be put on the rack, and I would tense my muscles, pretending to strain against my bonds as I pulled my limbs further and further away from my torso. I also imagined the 'bad-guy' watching me struggle and laughing evilly as he told me his evil plans...ah memories...
It's not exactly submissive, but I also remember playing with my dolls and barbies and polly pockets a big differently than the other girls in my class. I would have a bad guy or bad girl take my favorite doll and tie her to a chair. She would then kiss or do that weird barbie hump thing that passed for barbie sex before killing off the good guy to continue on to world domination. Mwahahaha.
Pain came into play when I was 15 or 16. I had developed a mild form of pica, where I had a craving for blood, so I would give myself little nicks then lick up the blood. To this day you can see faint scars on my upper forearm, but I've since stopped after I realized what it would look like to everybody around me should they discover the scars...
Well there we go. I'm actually glad I got all that out. Yay, I'm not too abnormal!