That depends on whether you're merely unable to die of natural causes or totally impervious to death. If it's the former, your head will lie on the ground (hopefully face up) as you use your final seconds to silently mouthe out some silly dying words like "oh my." But if you're unkillable, your body walks around in a big circle until your head sees it and guides the rest of yourself to pick up your detached noggin, all the while muttering "sonuvabitch, not again. I won't be able to turn my head or eat solid food for weeks."