I'm totally sure, but decided to write because I fell (accidentally) backwards off the stairs at a certain height and despite not having me a terrible height I fell from, apparently passively, makin g no attempt to grab hold of something. Anyway, I fell against a glass table, so if I'd banged my head it could've already been lethal. So it really depends not only how you fall and what you fall against, of course. For that, I ended up with three fractures in my spine, but I'm alive. If I'd fallen faceward, I think the injuries would've been less severe, because the immediate instinctive is to try to get hold of something and stretch your arms to break your fall.