OP: get checked out by a doctor, make sure you're all good.
If he'd had brakes, he'd at least have had the option of stopping the way 99% of people who ride bicycles do.
I'm just wondering where it was mentioned the OP does NOT have brakes? You guys are all assuming, just because of the bike and because the dude was attempting a skid, that he's running brakeless. Maybe he is, maybe he isn't - I run a front brake, but when doing a balls-to-stem skid (as the OP seemed to be trying) there's not much chance I could effectively use my brake when already committed to the skid. Get off the damn bandwagon already.
Someone else seemed to hit the nail on the head, OP got bucked off the bike either by bad form, bad balance, crap surface conditions or sheer unexpected power from the drivetrain.