Was there an R above its head and a green glow, with a totem of healing somewhere on the map?

Was it an elite, with regeneration?

I just tested, bloats do not naturally regenerate 16hp per turn, even if they are a regenerating elite. Bloats have 32 hp, and there are enemies in the sewers that drop the healing totems which heal everything affected by them by 50% of their hp. This would be a 16hp per turn heal, I am confident that is what happened.

There does not need to be mobs around. It was scheduled healing totem somewhere on that floor, they work from out of line of sight. Trust me, it was 100% a healing totem.