I had a vagal response from orthostatic hypotension once. Stood up (not even very quickly), took a step, realized I was getting dizzy (happens to me fairly often), tried to get to the doorway (three feet away) to brace myself, then woke up on the floor twitching, with stuff piled on top of me. (Took down a pile of crap in my computer room with me when I fell.) Got a big old lump on my head and some bruises, but no concussion or anything. Yay?