Let me say first I am not a medical professional.
Having said that, with what I do know of anatomy, you most likely 'popped' an intercostal ligament. It could also be the cartilage or ligaments attaching the ribs to the sternum, but the way you describe it sounds like intercostal to me. Not a broken bone, and it will heal but it may take some time.
I've never done this myself, but back when I first started grappling for MMA one of my training partners had this happen. I had him in a sort of neck crank (think the pinning position in collegiate wrestling, only I was cranking his head toward his stomach). He was a pretty solid dude, crazy ripped, and tried to muscle out of it. He felt (and I heard) a pop in his ribs, followed by a brief scream of pain. He went to the doctor, it was basically what I described above. He had folded one rib over the top of another, and that had strained the intercostal. He was off the mat for several weeks before he could do anything without pain.
Yours doesn't sound as serious, but who knows.