I think I know exactly what you're talking about. However, I'd say the problem is with the kill moves in general. Sometimes I think I have plenty of health left, but then bandits chops my head off with two handed weapon. I don't know of any console commands, but I know that there's a mod with an option to make player character immune to kill moves. It's the Dance of Death, a pretty popular mod. Toggling the option though MCM should make you immune to all the unpredictable kill moves done to you.