Why does this happen: Mobs with like 1 HP

[BradZax]

Am I the only one that's nightmares are haunted by an NPC you hit with a DD spell and got it to like 1 HP instead of killing it, and stops playing animations and charges at you sliding along the ground.

And while in this mode they seem to hit every swing for max damage?

Why does this happen? It's like my worst nightmare. And it haunts my dreams.