While I was fighting Diablo in Nightmare mode, I was almost dead. Ran over to a health pool and clicked it as he swung a hit at me that would have easily killed me. Instead of me living, I died, got full health, and was stuck being dead. He proceeded to kill my grave, and what was really funny was, he trapped me in his cage, picked me up, and the screen spasmed like it was having a seizure. After he killed me, my character appeared and I was stuck here. I had to leave the game and reload it in order to fix it. I don't know how particularly easy this would be to recreate, as it is about timing, but I'm sure it could be done. I was playing solo at the time. Sadly, I forgot to save the screenshot I got of this.

The way to reproduce would be:
1. Get to very low health, one hit and you will for sure die.
2. Click on the healing well just before you get hit.

You should gain full health, die, but not really die. Mobs still treat you as alive during this time of being "dead".