Immersive Healing

Below, you'll find a system of injury and healing that is gameable, but definitely a lot harsher than the system outlined in the PHB and DMG.  This is a system I came up with in the early days of 5e. I probably wouldn't use it as is now, but may revise it into something I would, later. I'm presenting it in case someone else finds use in it.  

Note that this variant is not geared towards a Morningstar: Age of Majesty campaign- many GMs will find that it will clash with the over-the-top themes of that setting. If you want a world of heroic action, it might seem contradictory to use healing and injury rules that are so harsh.

Rather, these rules are designed for gritty, low magic, or rare magic campaigns. Only use them if you want a world where injury leads to long term suffering in the absence of magic.

The primary consequence of these rules is to make magical healing more important to a typical adventuring party. This reinforces the role of clerics and others with magical healing as healers first, and may be unsuitable for some groups as a result.

A secondary result of using these rules is that there will be a lot more downtime between adventures. This may result in a slower progression for characters if the GM doesn't give roleplaying XP. If you do take the opportunity that this downtime presents to play out non-combat adventures, you will be rewarded with a rich campaign full of PCs and NPCs with deep personalities, where action is climactic rather than pedestrian.

Healing potions and other magical items can mitigate these consequences significantly, which may beg the question; why use these rules at all in those cases?   The one-word answer is "verisimilitude". NPCs and low-level characters won't have access to as many of these magics, and these rules will allow you to plausibly run an adventure with a PC or NPC that has a long-term injury. This can allow you as a DM to reinforce themes involving the banal evils of war (rather than just death), survival stories, or even cast your PC cleric as a true miracle worker when he heals a lame old man.

Variant: Immersive Healing

In this variant, the top 50% of your HP are still considered to be ephemeral- the result of luck, Grace, character experience, and psychological fortitude. The bottom 50% are actual injuries. Increasing hit dice represents your ability to turn serious blows into lesser ones, and to shrug off the psychological impact of facing death.

Even in this method, there are no negative hit points. Death saves and injuries while at 0 hp are handled as they are in the PHB.

Also under this system, short rests are unaffected- a character may spend hit dice normally to recover hp. When a character is healed to full HP, they receive all of their hit dice after a long rest.

There are three phases to healing in this method. They are presented here in reverse order, since a character will enter the last phase most often.

Phase 3- Psychological Recovery

When you are at or above 50% of your hit point maximum, you are rebuilding your confidence after facing death. You recover 1/2 of your hit dice at the end of every 1d4 weeks. You may roll these to recover hit points. Phase 3 ends when you are at full hit points.

Phase 2- Physical Recovery

When you are below 50% of your hit point maximum but above 0 hit points, you are recovering from your physical injuries to the best of your body's ability. You recover 1/2 of your hit dice at the end of every 2d4 weeks. You may roll these to recover hit points. Phase 2 ends when you are at or above 50% of your hit point maximum.

Phase 1- Regaining Consciousness

When you are stabilized at 0 hit points, you are unconscious, your body is battered, and you may be suffering from long term injuries. You may make a Constitution Save vs. DC 20 every 1d4 weeks to regain consciousness and 1 hp.

Another character may attempt to revive you with a DC 20 Medicine Check that they may make upon finding your body, and once every week thereafter. If your Constitution modifier is positive, they have advantage on this check, and if it is negative, they have disadvantage. If this Medicine check is successful, you regain consciousness and 1 hp.

Phase 0- Going Down

This part is *especially* optional. It's pretty nasty.

When you are brought to 0 hp or are injured while at 0 hp, you must make a Constitution Save with a DC of 10, or equal to the amount of damage you take that brings you to 0, whichever is higher. If you succeed, nothing special happens. If you fail, you take a long-term injury related to the type of damage that brought you to 0 hp.

You or the DM (DM's choice) should find the damage type of the injury. Use the type that dealt the majority of this damage, or decide randomly if there are multiple types that dealt equal damage. Find the type of the damage below and roll on its table to determine the long term injury. These long-term injuries can may be healed eventually or may be permanent, depending on the entry.

Long-Term Injuries

Acid

Roll   1d4.

1: Horribly Disfigured. -1d4 Cha. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

2: Respiratory damage. -1d4 Con. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

3: Dissolved fingers. You have disadvantage with your left or right hand (roll). The injury can only be healed by a Regenerate Spell.

4: Blinded. You have the blinded condition. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

Bludgeoning

Roll 1d8.

1: Mangled Leg (Lame). Roll to determine which. Your movement decreases by 5 feet. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

2: Mangled Arm. Roll to determine which. You have disadvantage with every action that involves the mangled arm. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

3: Concussion. -1d4 Int. Roll 1d100 to find the number of weeks until the injury heals.

4: Contusion. -1d4 Wis. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

5: Blinded. You have the blinded condition. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

6: Deafened. You have the deafened condition. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

7: Incapacitated. You have the incapacitated condition. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

8: Paralyzed. You have the paralyzed condition. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

Cold

Roll   1d6. If you duplicate a body part that has already received frostbite, increase the injury to the next stage.

1: First degree frostbite. Roll 1d4. 1=left hand, 2, right hand, 3=left foot, 4=right foot. This area becomes permanently insensitive to hot and cold, with no further effect. This injury can only be healed by a Regenerate Spell.

2: Second degree frostbite. Roll 1d4. 1=left hand, 2, right hand, 3=left foot, 4=right foot. Checks made using this area are at disadvantage. This area becomes permanently insensitive to hot and cold. This injury, except for the insensitivity to hot and cold, can be healed in 2d4 weeks, or a with a Regenerate spell.

3: Third degree frostbite. Roll 1d4. 1=left hand, 2, right hand, 3=left foot, 4=right foot. The body part freezes solid, and even after it thaws, it is useless for 1d12 weeks, and you will have disadvantage on all future checks with it. A Regenerate spell restores it.

4: Fourth degree frostbite. Roll 1d4. 1=left hand, 2, right hand, 3=left foot, 4=right foot. The body part freezes solid, and breaks off. A Regenerate spell restores it.

5: Anosmic. You may not longer perceive odors or tastes. This injury can only be healed by a Regenerate Spell.

6: Blinded. You have the blinded condition. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

Fire

Roll 1d4.

1: Horribly Disfigured. -1d4 Cha. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

2: Burned Lungs. -1d4 Con. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

3: Third Degree Burns. -1d4 Str. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

4: Mangled Leg (Lame). Roll to determine which. Your movement decreases by 5 feet. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

Force

Force damage may either deal no long-term injuries, or use the Bludgeoning table.

Lightning

Roll 1d8.

1: Arc Flash. Roll on the Fire Table.

2: Muscle Kinks. -1d4 Str. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

3: Spasms. -1d4 Dex. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

4: Brain Damaged. -1d4 Int. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

5: Brain Damaged. -1d4 Wis. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

6: Brain Damaged. -1d4 Cha. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

7: Explosive Grounding. Roll 1d4: 1=left hand, 2, right hand, 3=left foot, 4=right foot. You lose this appendage, and it can only be restored with a Regeneration spell.

8: Blinded. You have the blinded condition. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

Necrotic

Roll 1d4.

1:Withered Limb. 1d4: 1=left arm, 2, right arm, 3=left leg, 4=right leg. You lose this limb, and it can only be restored by a Regeneration spell. If you lose a leg, your movement decreases by 5 when you have a cane, or to 0 when you don't.

2: Necrotized Sinews. -1d4 Str. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

3: Weakened Heart. -1d4 Con. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

4: Sapped Spirit. -1d4 Cha. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

Piercing

Roll 1d6.

1: Grazed Heart. -1d4 Con. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

2: Blinded in One Eye. Roll to determine which. You receive disadvantage to checks involving sight. The Injury can only be healed by a Regeneration spell.

3: Deafened in One Ear. Roll to determine which. You receive disadvantage to checks involving hearing. The injury can only be healed by a Regeneration spell.

4: Lame. Roll to determine which leg is affected. your movement decreases by 5 feet. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

5: Sterilized. You may never have children. The injury can only be healed by a Regeneration spell.

6: Organ Damaged. You must stop to relieve yourself every 6d10 minutes, no matter what. The injury can only be healed by a Regeneration spell.

Poison

Roll 1d4.

1: Roll on the Acid table.

2: Roll on the Necrotic table.

3: Dyskinesia. You have involuntary muscle spasms that give you disadvantage on all Strength and Dexterity Checks. Roll 1d20. 1-12 is the number of months until the injury heals. 13+ the injury can only be healed by a Regenerate Spell.

4: Liver Damaged. From now on, any time you take poison damage, you take an extra 1d6 damage. Additionally, any time you drink alcohol or take another drug, it deals 1d6 damage to you per dose. This injury can only be healed by a Regenerate Spell.

Psychic

Roll 1d4

1: Phobia. You develop a flaw- a desperate need to avoid the type of situation or creatures even remotely similar to the one that dealt this damage to you. If you were damaged by a mind flayer, you might have a fear of octopodes. The DM will decide. When you are confronted with your phobia, all checks you make are at disadvantage. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

2: Philia. You develop a flaw- a desperate need to seek the type of situation or creatures even remotely similar to the ones that dealt this damage to you. If you were damaged by a Mind Flayer , you might feel compelled to obtain anything you come across with an octopus motif on it. If you ignore this flaw, you receive disadvantage to all checks made until the next day as you obsess over it. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

3: Fractured Mind. Create a new persona and alignment for two of your mental ability scores (Int, Wis, or Cha). The other one is what remains of your true self. Whenever you make a check with one of these two abilities, make a saving throw with your true self's ability score vs. a DC of 10 + your Fractured Ability score's modifier. If you fail, the other persona takes over. You adopt the personality traits of this persona until you successfully make a saving throw with one of the other abilities. You are at disadvantage with the other two scores while one is in control. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

4: Hallucinations. The DM will describe false sounds and images to you from now on, along with the real or illusory ones that are in the environment. You must treat them as if they were real. You may make a DC 20 saving throw to disbelieve them, and you have disadvantage to disbelieve this and other illusions. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

Radiant

Roll 1d2 (1d4/2).

1: Roll on the Fire Table.

2: Blinded. Your eyes shine with holy light, and it is the last thing you see. You have the blinded condition. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.

Slashing

1: Severed Hand. Roll to determine which. The injury can only be healed by a Regenerate Spell. Checks that require both hands are at disadvantage, and you may not make checks with this hand alone.

2: Severed Arm. Roll to determine which. The injury can only be healed by a Regenerate Spell. Checks that require both Arms are at disadvantage, and you may not make checks with this hand alone.

3: Severed Foot. Roll to determine which. The injury can only be healed by a Regenerate Spell. Checks that require both feet are at disadvantage, and your movement is decreased by 5 feet.

4: Severed Leg. Roll to determine which. The injury can only be healed by a Regenerate Spell. Your movement is reduced to 0 without a crutch, or by 5 feet with one.

Thunder

Roll 1d2 (1d4/2).

1: Roll on the bludgeoning table.

2: Deafened. You have the deafened condition. Roll 1d20. 1-16 is the number of weeks until the injury heals. 17+ the injury can only be healed by a Regenerate Spell.