PHB, page 292. Available in the SRD.

Unconscious

Condition

• An unconscious creature is Incapacitated, can't move or speak, and is unaware of its surroundings.

• The creature drops whatever it's holding and falls Prone.

• The creature automatically fails Strength and Dexterity saving throws.

• Attack rolls against the creature have advantage.

• Any attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature.