i remember one time i was having sex, and my girlfriend at the time was sitting right on top of me and leaned down to bite my nipple, causing me to reflex in such a way that my back arched, which threw her off of me rather violently. she hit her head on the nightstand, creating a nasty bruise.

she was ok. thankfully. and, i don't blame myself - i reflexed, it was involuntary.

but, if she had landed a few cms one way or the other? yeah - it could have killed her. certainly.