Below 0 HP, a creature is Dying and loses 1 HP at the end of each of its turns.
A creature dies when its HP is at or below negative its current Constitution score.
Healing
Healing cannot raise a creature above its maximum HP.
Stabilizing
A successful Heal check can stabilize a Dying creature, bringing it to 1 HP and ending its loss of 1 HP per turn. A creature stabilized this way remains Unconscious. It wakes when it receives further healing or completes a Short Rest.