Well, an update on my situation: two weeks ago I was self sucking, and I was really pushing myself, going very deep and getting almost all of my cock in my mouth, to the point of gagging on it (my cock head was hitting the back of my throat), which I've done a few times before. All of a sudden I heard this CRACKING sound in the middle of my back! Coupled with a little bit of pain, but nothing major. It sounded like someone cracking his knuckles. I never heard that from my back before EVER! I was scared to hell that I broke my spine or something. I of course immediately stopped self sucking. An examination of my back didn't reveal anything unusual, other than about 2 or 3 of my vertabrae on my spine on my lower middle back were painful to the touch. No other back pain from standing, etc., unless I bent over as to touch my toes or self suck, then it hurt. It's been 2 weeks since that incident, and those vertabrae still hurt a little if I touch them, but otherwise no pain or problems. It hurts if I try to bend over in the self suck position, so I stopped all attempts at it for now. I'm not sure what I did to my back, but it's probably nothing good. I'm going to lay off self sucking for a long while (at least a month or two), and let things heal. And when I resume, I don't think I'll be deep throating anymore. So, to answer the original question, yes you can injure yourself self sucking!! Although this is the first injury I got from it, and I've been self sucking for over 13 years.