Why did I bleed during sex??

Hi ladies,
So last night I went home with this guy I've been seeing after a night out. We eventually made it back to the bedroom where we were having a veryy fun time. I wasn't in pain at all, in fact it had been a few months since I've had sex so I was having a great time. We were alittle rough but nothing crazy by any means necessary.. Anyways, at one point he was on top, completely normal when he asked "wait a minute.. Are you bleeding?" I automatically answered "what? No" since I was in no pain at all and I'm no where near my time of the month. But low and behold, I look down and there's just a beautifully bright red stain on his bed, as well as on me and him. I immediately became embarrassed.. He was very sweet about it and cleaned up as I went in the shower. I checked myself out alittle bit and there was no cuts, pains or anything of the sort down there, and soon after I stopped bleeding. Needless to say we were done having sex for the night after that, but I am extremely conserned as to what that could have been! That's never happened to me before so I'm not sure if anyone has had a similar experience. I plan to make an appointment with my GYNO ASAP. ANY FEEDBACK WOULD BE APPRIEACTED.