Wow okay. The wording makes it sound like you will come back to life. Still though, I haven't seen it proc. I will have to pay closer attention.
id imagine it has something to do with the fact that undead cannot be healed.. thus the healing to 20% doesnt happen.
so it goes something like this.. you get attacked and "killed" you receive +20% healing... which does damage to you instead due to being undead thus killing you anyways.