Schrodinger's Hit Points

What exactly do hit points represent?

That seems to be a subject of constant debate ever since the original game hit the shelves, but it became more complicated once 4th and 5th edition D&D introduced two new concepts into the game: First, the idea of a pool of "hit dice" that a player can use to replenish their hit points during a "short rest"; and second, the idea that all hit points (and hit dice) are restored to full after a "long rest" of a night's sleep.

Now granted, the official explanation in 1E was always that hit points represented not just physical injury, but also a combination of skill (twisting so that the sword thrust that would have impaled a 1st level character inflicts a mere scratch), luck, magical protection, and divine favor. But as a matter of describing the effects of the loss of hit points in play, we tended to describe a slow build-up of scratches and bruises which would become gashes and major blunt-force trauma (or burns, or whatever) as the character's hit point total dropped. A cleric or druid's healing spells were therefore assumed to cause these actual wounds to fade right before one's eyes in miraculous fashion. Ditto healing potions.

The role of a cleric in restoring hit points on the fly was so critical that the class was all-too-often reduced to that of "heals-on-wheels." This was particularly bad in 3rd edition, where every spell level had its associated cure . . . wounds spell. (At least in previous editions the cleric had some spell levels with no healing spells in them, so they could use those for other functions even if they wanted to load up on healing spells.) Fourth edition was specfically designed with the idea of using "hit dice" to restore hit points and getting everything back after a long rest just to rescue the cleric class from the team medic role--and to rescue groups from the necessity of having a cleric or druid with them whether anyone wanted to play one or not.

Since the characters using hit dice weren't just regenerating like trolls (or Wolverine) whenever they used hit dice, obviously hit points represented fatigue more than actual injury. In fact, 4th edition introduced the concept (important for certain abilities and actions) that a character only became "bloodied" when they were reduced to half their hit points. This represented the point at which they suffered their first real wound. Thus, using hit dice when resting was basically just getting one's wind back, not healing per se. This is expressly described in the 5th Edition Player's Handbook (p. 197):

Dungeon Masters describe hit point loss in different ways. When your current hit point total is half or more of your hit point maximum, you typically show no signs of injury. When you drop below half your hit point maximum, you show signs of wear, such as cuts and bruises. An attack that reduces you to 0 hit points strikes you directly, leaving a bleeding injury or other trauma, or it simply knocks you unconscious.

All well and good, but it leaves open some questions:

1. Why does being reduced to zero hit points always result in unconsciousness? Plenty of life-threatening injuries that take a person out of a fight would leave them conscious--though perhaps in too much shock to react (effectively unconscious), or perhaps just laying in the field, fully aware but clutching a broken limb or clamping down on a deep gash.
2. Why, if being reduced to 1/2 hit points leaves you bloodied and bruised and being reduced to 0 hit points means a serious, even life-threatening injury, is sleeping it off enough to completely restore all hit points? (Besides making it so that you can jump right back into the game.)
3. If you only receive your first actual injuries at 1/2 hit points, why do you need to make a Constitution save against poison when "bitten" by a asp before that? You can sort-of justify this, but it starts to feel like a lot of meta-gaming to do so.

So many effects surrounding hit points, wounds, and healing can only be described after the fact in 5E: A character takes a hit from an orc's greataxe that takes him to zero hit points. He falls to the ground "unconscious" and starts making death saves. If he makes three saves, he becomes stable and wakes up some time later with 1 hit point--and after a short rest, can get back more hit points via hit dice. If he fails the saves, he dies. So the question is: What exactly was the actual injury that took him out of the fight? How should the DM describe it?

Until we roll those saving throws, we don't know. We can't know. If the player rolls high, he might have lost consciousness from a glancing blow partially deflected from his helmet, or perhaps have taken a terrible gash to the leg that thankfully missed his artery. If he rolls low, maybe that same glancing blow caused a terminal brain injury or the axe severed an artery, causing him to bleed out in minutes. Either way, the DM is reduced to describing the injury in the vaguest of terms--perhaps even just the mechanical results--until the dice rolls reveal what happened after the fact.

From a purely gamist perspective, these are all acceptable breaks from reality. But from the perspective of a DM who loves using narrative to make the world feel "real," it falls into the trap of dissociated mechanics. Not in a way that has to ruin the immersion in the game, but in a way that leaves me as a DM wondering, "Is there a better way to think about this?"

The Math

Death saves are the only saving throws in the game that are never influenced by any outside source. They are not dependent on Constitution, there is no possible proficiency bonus, nor is there any magical effect (other than healing, which automatically restores the character to 1 hit point) that helps in any way. When you get down to it, this means that any time a character is reduced to 0 hit points, barring intervention by his allies, there's a 50/50 chance that the wound was lethal (barring instant death from massive damage), and a 50/50 chance that it removed the character from the fight but was quite minor in the grand scheme of things--a broken bone instead of a severed hand. 

There are some slight modifications to those odds, reflected in rolling a natural one (counts as two failed saves) or a natural 20 (instantly restores the character to 1 hit point), but the basic essence of the math is simple.

That being the case, why roll three times at all?

The answer is to create tension. As another PC, you don't know if your comrade will die in two rounds (due to a natural 1), die in five rounds, stabilize and wake up in a few hours, or suddenly wake up able to act (due to a natural 20). The death saving throw gives you a ticking clock of unknown duration in which to treat your companion. Handled right, it can create some wonderful dramatic moments as other PCs race to try to save their friend--especially if an enemy is still adjacent to said friend and is intent on delivering the coup de grace. 

From a strictly gamist perspective, this is brilliant, driving action and creating suspense. But from a narrativist or simulationist perspective, it becomes difficult to describe exactly what happened the moment a character hit zero hit points. The PC becomes a weird version of Schrodinger's cat--neither alive nor dead, neither spurting blood or merely stunned from a blow to their helm--until the post hoc die rolls say so.

So how do we "fix" this (for those of us pedantic enough to think it needs fixing)?

House Rule: Single Death Save

At the time a character reaches 0 hit points, the Dungeon Master takes the player aside and has them roll three dice: a simple 1d20 roll, a Constitution saving throw, and a d4. The results are compared to the following table. (Edit: I modified this after realizing that the odds of rolling a 20 in three chances or a 1 in two were slightly different than the odds of rolling either in just one attempt.)

d20	Result
1-2	The character is critically wounded. Roll on the Lingering Injuries table* to determine the location of the injury. The character dies in 1-2 rounds (1d4/2) unless someone intervenes. The character is Unconscious.
3-5	The character is critically wounded. Roll on the Lingering Injuries table*. Without intervention, the character will die in 1d4+2 rounds. The character must make their Constitution save or be rendered Unconscious; otherwise, they are Incapacitated.
6-10	The character is severely wounded and suffering blood loss, internal bleeding, or shock (depending on the cause of injury). They will die in 1d4+2 rounds without intervention, but do not need to roll on the Lingering Injuries table. The character must make their Constitution save or be rendered Unconscious; otherwise, they are Incapacitated.
11-17	If the the character fails their Constitution save, they are knocked Unconscious for 1d4 hours. If they succeed, they are Incapacitated for 1d4x10 minutes. If they roll a natural 1 on their save, they are Unconscious for 1d4 hours and must roll on the Lingering Injuries table*. At the end of their period of being Unconscious or Incapacitated, they regain 1 hit point and are able to act normally.
18-20	The character is Stunned for 1d4 rounds, after which they recover 1 hit point and can act again.

* See the DMG, p. 272

The player is not allowed to communicate the results of this roll to the rest of the party if they are Unconscious, but may if they are merely Incapacitated. The DM determines what the party sees see based on the circumstances (who is within visual range, the type of damage dealt by the enemy, a roll on the Lingering Injuries table, etc.) and describes it accordingly. 

Additional damage suffered while at 0 hit points requires another roll on the above table. If the character is already dying, the additional injury will at a minimum shorten their remaining life by one round. Under certain circumstances, the DM may rule that a second roll that results in a 1-10 on the above table results in instant death. (E.g., the foe cut their throats.)

In some cases, this will play out exactly the way rolling multiple death saves does in the core rules: The character is unconscious, and the party has an unknown amount of time before they either wake up or die, resulting in a race to heal them. In other cases, it will play out differently: A character clutches the severed artery in their wrist, calling for help as they bleed out. Another receives a vicious blow on their helmed head, resulting in a momentary blackout, after which they rise and attack an unsuspecting foe to turn the tide. Still another receives the exact same blow, but an unseen internal bleed insures that they never awaken. Characters who are incapacitated might still be able influence combat; e.g., spotting a foe behind an ally who is using Stealth to close in and launch a sneak attack.

Certain results on the Lingering Injuries table would need to be adjudicated according to the above. A character who is really dying may well have lost a hand, arm, or leg. One who is not probably suffered a fracture or deep cut that severed the tendons instead. A Lingering Injury inflicted by fire will obviously play out differently than one inflicted by the blow of a mace. In all cases, the DM will need to look both the cause and the results and describe accordingly. The DM should bear in mind that ancient and medieval weapons were rarely capable of completely severing limbs, so a result of "Lose an Arm or Hand or Foot or Leg" might simply indicate damage that, barring magical intervention, would require amputation of the limb in question to save the character's life. Generally speaking, complete amputation in a fight should only occur when the "remaining damage" (see PHB, p. 197) after a character is brought to 0 hit points is significant. 

Always remember that the goal of the game is fun. A character with a cool scar (or three) is fun. Characters who lose a leg might not be. Unless all of the players are agreed that the game should be in Legendary Hard Core mode, always interpret the rolls as benevolently as possible. 

This applies to important NPCs as well. While most "mooks" will simply fall and die at 0 hit points, a major NPC should roll on the table exactly like a PC, with the DM needs adjudicating accordingly. This could result in some spectacularly scarred and maimed NPCs seeking revenge for their injuries. 

That's what we call a plot point.