From the AD&D DMG, p 82 (read closely, paying particular attention to what's inside the parentheses):
When any creature is brought to 0 hit points (optionally as low as -3 hit points if from the same blow which brought the total to 0), it is unconscious. In each of the next succeeding rounds 1 additional (negative) point will be lost until -10 is reached and the creature dies. Such loss and death are caused from bleeding, shock, convulsions, non-respiration, and similar causes. It ceases immediately on any round a friendly creature administers aid to the unconscious one. Aid consists of binding wounds, starting respiration, administering a draught (spirits, healing potion, etc.), or otherwise doing whatever is necessary to restore life.
Back when 4e D&D was a thing, I took part in discussions about the DC for a Diplomacy check to permit an ally to spend a Healing surge.