I've had something like this happen before. I don't remember what I was doing but I pulled like my back like this and it hurt so bad. I couldn't sleep right for a few days I was uncomfortable no matter how I would lay. I think it was just a pulled muscle, the pain did go away after a few days. If it still hurts in a week I would definitely see a doctor though. You could try to put some Bengay on it and see if it helps.