Let's say Garry has 15 max HP and his current HP is 3.
Scenario 1: An enemy with 2 attacks a turn hits twice, dealing 12 damage the first time and 6 damage with the second attack; technically, the enemy did deal 18 damage, which is equal to Garry's max HP. Is Garry instantly dead, or is he still alive because the damage wasn't all from a single hit but 2 hits?
Scenario 2: Garry walks into a room with 3 archers who readied attacks to shoot him. First archer deals 9 damage, second one deals 9 more, and third one deals 3. Is Garry dead since it all hit him at once, or not since it was all from different people and attacks?