Hit points are a pretty abstract thing... you risk conceptualizing them as ‘meat’ this way

Also, there are some strange results at the extreme ends... a low level wizard can fight fine until literally their last hit point, whereas a max level Barbarian may suffer penalties for 40+ HP?

And how does this interact with existing exhaustion rules? Does it make frenzy Barbarians even more prone to dropping over dead? Or make Sickening Radiance notably more fatal?