Stacked it, yes means fall over.
I’ve had a major fall off handle bars, my mate was dinkying me (BEFORE YOU ASK THAT MEANS I WAS SITTING ON THE HANDLE BARS), and we were going down a hill and I yelled CAR, and she put the brakes on and I went flying, I was lying in the middle of the road for about 30 seconds before I realised what had happened, when I finally came out of it, I pissed myself laughing, I thought it was so damn funny. I only ended up with grazes and bruised ribs. Oh and my mates tyre just about went up my ass too. Like rode straight over me, that would have been pretty funny, Major BIKE RACK.