When you drop to 0 hit points, you either die outright or fall unconscious, as explained in the following sections.

• Instant Death
  • Massive damage can kill you instantly. When damage reduces you to 0 hit points and there is damage remaining, you die if the remaining damage equals or exceeds your hit point maximum.
  • For example, a cleric with a maximum of 12 hit points currently has 6 hit points. If she takes 18 damage from an attack, she is reduced to 0 hit points, but 12 damage remains. Because the remaining damage equals her hit point maximum, the cleric dies.

• Falling Unconscious
  • If damage reduces you to 0 hit points and fails to kill you, you fall unconscious. If you receive healing while unconscious, you may choose to wake up and instantly pick up any items you were holding before falling unconscious (provided those items are still within reach). If you choose not to wake up, you are stabilized, and can choose to wake up the next time you receive healing or a successful medicine check from another creature.  This unconsciousness ends if you regain any hit points. 

• Death Saving Throws
  • Whenever you start your turn with 0 hit points, you must make a special saving throw, called a death saving throw, to determine whether you creep closer to death or hang onto life. Unlike other saving throws, this one isn’t tied to any ability score. You are in the hands of fate now, aided only by spells and features that improve your chances of succeeding on a saving throw.
  • Roll a d20. If the roll is 10 or higher, you succeed. Otherwise, you fail. A success or failure has no effect by itself. On your fourth third success, you become stable (see below). On your fourth third failure, you die. The successes and failures don’t need to be consecutive; keep track of both until you collect four three of a kind. The number of both is reset to zero when you regain any hit points or become stable.
  • Rolling 1 or 20. When you make a death saving throw and roll a 1 on the d20, it counts as two failures. If you roll a 20 on the d20, you regain 1 hit point.
  • Damage at 0 Hit Points. If you take any damage while you have 0 hit points, you suffer a death saving throw failure. If the damage is from a critical hit, you suffer two failures instead. If the damage equals or exceeds your hit point maximum, you suffer instant death.

• Remaining Unconscious After Healing. If you receive healing and choose to remain unconscious, your death saves are reset to 0, and you do not make any more death saves until you drop below 0 hit points again.

• Wound Condition
  • The wound condition is gained after a creature that was at 0 hit points receives hit points and wakes up. This condition is also gained if the creature that was healed chooses not to wake up immediately, but only once it eventually does wake up.
  • This condition is cumulative. Each time you receive it, you gain 1 level of wound.
  • When a creature with a level of wound is reduced to 0 hit points, they are considered to have failed one death saving throw already for each level of wound it has.
  • When a creature with a wound takes a short rest, it can expend a hit dice to remove a wound it currently has. This can only be done once per short rest.
  • When a creature with a wound takes a field rest, it can expend a hit dice to remove all wounds it currently has.

• Stabilizing a Creature
  • The best way to save a creature with 0 hit points is to heal it. If healing is unavailable, the creature can at least be stabilized so that it isn’t killed by a failed death saving throw.
  • You can use your action to administer first aid to an unconscious creature and attempt to stabilize it, which requires a successful DC 10 Wisdom (Medicine) check.
  • A stable creature doesn’t make death saving throws, even though it has 0 hit points, but it does remain unconscious. The creature stops being stable, and must start making death saving throws again, if it takes any damage. A stable creature that isn’t healed regains 1 hit point after 1d4 hours.

• Monsters and Death
  • Most GMs have a monster die the instant it drops to 0 hit points, rather than having it fall unconscious and make death saving throws.
  • Mighty villains and special nonplayer characters are common exceptions; the GM might have them fall unconscious and follow the same rules as player characters.