TMI: Sudden Bleeding during Sex?!

So, the title pretty much says it; my husband and I were "gettin it ooon" tonight. 😍 
I was on top and facing forward.
I got off to turn around and BAM! Blood! Bright red blood! 😱😱😱 All over both of us! What?! 
I didn't feel a thing. 
He didn't feel a thing. (Just ruling that one question out; we're positive it came from me.)
Suddenly, BLOOD! And not just a little. LOTS! 
We joked about how lucky he was to get a virgin again; but here's the thing: We've had sex 2-3 times a week on average for three years. Nothing virgin there. 
I stuffed some Kleenexes up there and hustled to the bathroom. We both got cleaned up, and I donned undies with a nice, thick maxi pad on them. 
10 minutes later, I decided to check the progress, and guess what? NOTHING. No more blood whatsoever. Not a spot on the pad. 
 
So...? Any ideas? 
Did we, um, pop something? 
I'm scheduled for my physical in two weeks, so I'll bring it up then; but if anybody has any ideas, thank you!
(I don't know if it matters, but I am 24, 5' 3" and 150 lbs. Just in case that gives any clues.) 🙇🏻
Thank you! 🍰
EDIT: I am also smack between periods. Like, right in the middle.