When player falls unconscious his body glitching into running at the spot where he supposed to be lying on the ground. Sometimes body is standing or running repeatedly a short distance till the moment he dies or respawns, after that his body remains on the groud but for a short time then it disappears. I've been playing scince alpha release and I've never seen an unconscious player that was lying on the ground as he supposed to, so for me it happens pretty much always.