Taking -ve damage when mortally wounded

[Ian]

[HP=-11/MA=10]:
Crypt, Shadowed Hall
Also here: wight, wight.
Obvious exits: north, south, east, west
The room is dimly lit
The wight swipes at you with its claws!
The wight slashes you for 3 damage!
The wight slashes you for 5 damage!
Your life is drained for -14 damage!
The wight slashes you for 1 damage!
Your life is drained for -5 damage!
The wight swipes at you with its claws!
The wight swipes at you with its claws!
[HP=-1/MA=10]:

This was so awesome, I waited about 20 or 30 rounds.  Didn't get revived in the end unfortunately, that is as close as I got.

[The Crazy Animal]

I've noticed this in a few other places around the room on spells cast by mobs I'm not sure exactly whats causing it yet...