Something like that happened to me in first grade. I was trying to go down a slide and a friend decided to climb the slide itself. He ended up launching me off the side of the slide. It was maybe a five or six foot slide, and I remember going over the side in slow motion, grabbing for the rim of the slide but being at least 6" away from reaching it, and then suddenly.. sharp pain and pitch black as I landed on my back.

I was conscious again about 10-15 seconds later. It's the kind of thing that sticks with you your whole life. It probably wasn't close to life threatening, but the combination of adrenaline, sharp pain, and brief unconsciousness definitely leaves an imprint in your memory.