As a warrior, if you perform Sweet Revenge when downed, you’re given a chance to return and try to fight. If your enemy dies, you can stay alive. If not, you die.
But this bug appears in two occasions:
1) If the person you’re attacking doesn’t die. For example, this person was hypnotized into fighting you and is not really a bad guy. Since he turns back into a good guy at the end and doesn’t die, your timer continues on your sweet revenge and at the end of it, you die.
2) If you’re in your story quest and you hit Retry at checkpoint, for some reason the timer continues if it wasn’t up, and you fall over dead again.
I’m not sure if in these instances, your armor damages, but it seemed like a bug to me.