When I was about 20 weeks, DH, DD1 and & were playing on our bed. DH went to tickle DD1 and she fell backwards right onto my belly. The pain was really bad for a while but I never got any discharge. The pain hung around for a day or two so I went and got checked, like starbright said I could not stop thinking about it and thought better to just get checked and know. Everything was fine thankfully. By you posting means your worried and that to me is your answer, go get checked. If you want to wait till tomorrow ring your GP, tell them what happened and they might make room for you, if not call your hospitals birth/Maternity ward and talk to someone there. Ease your mind I say.