Fun fact about going below 0 HP: Third Edition D&D tracked that. At 0 you were staggered, below that unconscious, and at -Con Score negative HP you died.

This being D&D 3.x (3.0/3.5/Pathfinder 1e), there were abilities that extended that limit, abilities that let you stay conscious below 0 HP. I’ve seen someone play a build that was always at negative HP, with a limit of something like -300 before dying, and got bonuses for being in the negatives.