Vivian Abraham c.2001?
Hit points represent your character's ability to avoid lethal damage. When you reach zero hit points or go negative, you gain a negative condition at the discretion of the GM. For example:
Grignr the Barbarian faces off against Sargon the Sorcerer in the public arena, a dispute over the ownership of some gem. Grignr fells Sargon with one mighty blow of his axe, slamming them to the ground. Sargon's leg is broken, reducing their move rate and giving him -2 on all rolls, including their concentration check to cast due to the excruciating pain. Sargon musters their strength, makes their concentration check, and casts a maximized Sound Burst on the hapless Grignr, knocking their below zero. They make their Fortitude save against the stun effect of the spell, but now has a concussion, lowering their rolls by 4, including their initiative while they desperately attempts to clear their head. Grignr aims another mighty blow at Sargon, critting again, and neatly splits them in half.
Hit points heal fast. With an hour's full rest, you'll get them all back. Conditions require more work. Simple conditions like a light fracture or a minor burn can be alleviated over time with an appropriate Heal check or immediately with a cure light wounds. More serious conditions require more time, better Heal checks, or stronger healing spells.
Healing spells still cure the same number of hit points. For example...
The spell Cure Serious Wounds has two effects. First, it can be used to cure a number of hp. Second, it can be used to remove certain negative conditions, such as a broken bone, If someone has no hp and has a broken bone, Cure Serious Wounds will both heal the broken leg AND heal hp. If a Cure Moderate is used, it will only heal the hp damage, not the broken leg. Proper application of the Heal skill, together with rest, can downgrade negative conditions over time. So if you broke your leg a few days ago, had it set and splinted, and haven't been walking on it, it could be downgraded to a moderate wound.
Side note - feats and abilities that affect negative hit points will need adjustment. For example. Die Hard now allows you to ignore a single negative condition.