I can empathize, was inter-tubing at a cut through on a main highway when salt truck came by and plowed the snow off the road, leaving a two to three foot drop and creating a ramp. Me and my friend go to the highest point and ride down together, we were zooming down everybody watching us. Well we hit that snow ramp and back flipped upside down, me landing perfect on my ass on freshly plowed asphalt with no snow cushion. Needless to say I broke my tailbone and almost blacked out from the pain. Saw stars in my vision for thirty minutes. Stood by the fire the rest of the night trying not to move.