Depends. If you take enough damage to put your HP to 0, then you're downed. But if the damage is enough to reduce your HP in the negative equal to bloodied HP value. So, a character with 50HP would have 25 bloodied HP. They take 75 points of damage: insta-death.
In this case, the main character...
It is so infuriating to see the MC live as a slime. As I understand it, they're always nagging away as voices in his head. He could tell the old assholes to shut the fuck up. Or ask around for a way to get the curse removed. You know, getting rid of the useless junk draining your mana away. But...