In standard Dungeons and Dragons when dropped to zero hit points, characters can quickly get back to their feet with a simple level 1 spell. The battle fatigue option changes that. When a creature drops to 0 hit points and is healed back to consciousness, they suffer a level of exhaustion to reflect the injuries they've sustained and the shock of being forced back up. This level of exhaustion can also stack, making falling unconscious more perilous to the character.