Well, sort of...
I don't know that there is a "bug" involved, but I have two game sessions where my character was suddenly dead under circumstances when I didn't expect it.
In the first case, I was running along a sluice in the area outside the starting mine tavern when I fell off and died. Trouble is, the fall height was not significant. In fact, I went back and ran up and down the sluice, jumping off in multiple locations, both as close to where I fell off as I could remember as well as points with an apparently greater height. I survived every "fall." Well, "no biggie." I wrote it off to possibly being impaled by a stalagmite and moved on.
The second time, I was in another mine killing pit rats while looking for what needed to be done to block them from swarming. I seemed to be taking the hits without much trouble until, suddenly, I was presented with the option to load a previous save -- i.e. I had been killed. This time, I resorted to the console trying to verify that I had died and to puzzle out how. Turns out my level 2 character with 88 maximum health had -27.something health. O.K. Dead. So, I "resurrected." Well, sort of. I couldn't stand, but I was "alive" and could both kill rats with my invisible sword and cast healing spells while lying in a crumpled heap on the ground. While not ideal, it was trivial to stay "alive" killing rats while watching in third-person -- I normally play almost entirely in first-person which makes it less obvious that I have fallen to the ground dead when that happens.
So, with the long-winded background out of the way, is there some kind of "devastating" hit mechanic at play? If so, it seems pretty overpowered is some cases. Sure, people can die from low falls and perhaps even rat bites to a vital artery -- though it seems likely that healing spells or potions should be effective before bleed out leads to unconsciousness. Still, is that what might be happening? If so, is it "working as intended?"
Note, I generally play first-person RPG type games as dead-is-dead -- i.e. permadeath. Granted, that is my personal gaming psychosis and self-inflicted, but the platforming nature of Nehrim in the early going -- i.e. immortal NPC which must be evaded by learning the correct path until it can later be almost trivially killed by the "right" method -- makes this sudden death possibility even more "challenging."