Thanee said:
Hit points have no relation to exhaustion/wounds in any way, even at 0.01% hit points you are totally fine.
Here's a post I made in regard to this topic on the old D&D-L back in 2000:
I've always thought of hit points as luck and fatigue. When the high level character is struck (or fails a save) for 20+ points of damage, it could be physical but usually I describe it as no real damage. Instead, it represents the character avoiding damage and using luck and skill to survive.
However, the character's luck has a finite and measureable total. When it reaches say, 10 hp, he has some wounds, but more importantly, tempted fate many times and should take it easy. Usually this calls for a retreat from the situation to "heal."
The various cure wounds spells heal some wounds but mostly invigorate the "wounded" character with positive energy represented by recovered hit points. The character's "luck" total is restored and may safely resume risking his neck, relatively confident of his skills and the "favor of the gods" to keep him from death.
The application of what hit points represent should always change given the situation and the type of "damage" the character sustains. In the end it is the DM's call to describe it, but the mechanic gives the player and referee a concrete reference point for the amount of punishment, stress, fatigue, and plain old luck the character can endure before death.
For example, while very strong, Conan's greatest attribute was his barbarian background that gave him incredible quickness (usually described as panther-like), and a sort of "sixth sense" (kind of like Spider Man) that allowed him to avoid damage that would kill him.
In D&D terms, when Conan takes 50 points of damage and has, say, 50 hit points remaining, he actually avoided the giant's boulder through reflexive agility. The 50 points of "damage" is for game play, so that Conan will not be Superman and escape harm indefinately. The hit points represent the general reliability of Conan's quickness and panther-like reflexes to avoid real harm. However, if his hp total reached around 10, he is either tired or has tempted fate too many times. The low hit point total is a concrete
clue to the player of Conan that it is time to take it easy. I also add that if one were to make Conan a D&D barbarian, his agility and "sixth sense" would be represented by the d12s for hit points and the uncanny dodge ability.
In other game systems, like GURPS, the realism of the game mechanics makes a single roll of the dice enough to end a mighty hero's career, with no forwarning. The purpose of the high total of hit points for high level characters is to allow the player know how much he is risking each time he goes adventuring, and when to retreat. The high hit points allow the player to act, with some confidence, like a hero.