Keefer,
I ruptured the muscle membranes in both arms, mostly the forearms it seems, from doing assisted pull ups for ten minutes in a strength conditioning class at a local gym. Basically tore open the sheaths that encase the muscle tissue. Caused by overexertion on that muscle group. Never even knew you could do it. Kind of like having a bunch of internal cuts I guess. Main concern now is scar tissue, nerve damage and recovery. Not sure how it will affect my strength in the long run.
I'm no doctor but what you have sounds like a pulled or torn muscle. Maybe an oblique? See a doctor if you haven't already. Don't ignore it. Pains like that need to get checked. Let me know what you find out and I wish you a speedy recovery as well.
John