I did a search once becuase I was with a guy and that happened but it was a lot! It scared the sh*t out of me. Don't want to scare you, but you need to see your doc. Could be nothing but it could be something BIG. Good luck
I had that happen to me... twice... both times it was after a bad cold/throat infection ... so it may be just that you're run down.. drinking a lot will do that..
You probably had a Penis Polyp (hemmeroid inside Penis) burst. One question, were you fuck-squatting her? The reason I ask is because it happens when you lift heavy objects while erect. I'd play it safe and see a doc. He/she may have more insight.