I used to play a cleric in Everquest. We used to play the 'purple bar game'.

If you drop to 0 hp, you fall unconscious, but you're higher than, if I recall correctly, -20, you don't die. Instead, you bleed for a few hp per second until you reach that threshold (or, more frequently, something hits you). When this happens, your HP bar turns purple.

We used to make it a game to try and time heals so they didn't land until the tank was unconscious. It resulted in many, many deaths.