If your HEALTH is dropped below 0 on a trap when exiting a dungeon, you do not die, you may live. I was poisoned by a trap on the sarcophagus on the way out of Targoth's and suffered poison damage and damage over time so I had -4 HEALTH and walking about like normal. However, this is not normal. I will try to do some other things in my undead state.
A trap is tripped when MECHBlack opens the Sarcophagus!
MECHBlack gains 4 poison (4 total). MECHBlack is hurt badly!
MECHBlack loses 2HP to poison.
MECHBlack loses 2HP to poison.
MECHBlack loses 1HP to poison.
MECHBlack loses 1HP to poison.
MECHBlack loses 3HP to poison. MECHBlack is about to die!
I was able to Look At my character sheet, interact with environment objects, open my inventory window and all while negative HEALTH. My next problem is that taking poison damage from a trap going through a dungeon door will kill you if the timing is right. For example, if timed to take damage after your character appears on the other side, even miliseconds, you will die. However, if timed so that you reach 0 HEALTH the exact moment you move screens, you get frozen in Limbo. Which brings me to where I am now. Frozen between screens, 0 HEALTH and no options to Try Harder, or a cursor to click anything with. Funny ;>
Update: This is negative HEALTH issue is repeatable. I duplicated this bug just before the time of this post.
Note: I was able to run to the next screen, enter combat with an imp at -24 HEALTH. The summoned ratling was slain as my character's options only allowed for guarding. It did not allow me to move, attack, or use item. But, I ended up being slain by the imp with a direct damage spell. That death was real. I may attempt to heal myself if I can get this bug to trigger again.
Multiple posts, I apologize, but in the recent test I have a video of starting combat with negative HEALTH and taking melee hits from mobs, living, and winning the battle. This happened for a few fights. There could be some threshold or something unseen or displayed incorrectly even in HEALTH. When I reached -33 HEALTH, I died for (again?). So, it does have its limits, but it is repeatable and may be only a display in HEALTH bug.
I am consistently able to replicate the issue. It's a bit funny, but I hit negative health about equal to half my maximum health before I officially (die) again. This value is nearly equal to the health I receive after reviving. However, in this last case, I had regenerated up to positive 11 before being struck down at -47, guarding, killing and takings hits at -39 health even. Anyway, I hope I have provided enough information for you to look into and if you would like to see this (if you are unable to replicate this yourself), I can share my footage with you.