Damage, Dying, Death
Most creatures die the instant they drop to 0 hit points. (98). But player characters and, if the GM wishes, special nonplayer characters and mighty villains follow these rules:
Dropping to 0 hit points kills you instantly only if the damage is massive.
If damage reduces you to 0 hit points and fails to kill you, you fall unconscious. This unconsciousness ends if you regain any hit points.
Whenever you start your turn with 0 hit points, you must make a death saving throw to determine whether you creep closer to death or hang onto life. Special rules apply if you take damage at 0 hit points.
A stable creature doesn’t make death saving throws, even though it has 0 hit points, but it does remain unconscious.