Fatigue is a measure of exhaustion. It's built up through actions that cause Encumbrance, such as attacks and spellcasting, but certain attacks or magical abilities can add Fatigue in large amounts. Most non-Divine spells also add large sums of Fatigue to the caster. Unlike damage to Hit Points, it is not innately lethal.

• Every 10 Fatigue a unit has, reduces their effective Defence Skill by 1.
• Every 20 Fatigue a unit has, reduces their effective Attack Skill by 1.
• At 50 Fatigue or more, a unit is three times more likely to suffer an Armor-defeating hit.
• At 100 Fatigue or more, a unit is unconscious; they cannot move, and they are helpless.
• A unit cannot have more than 200 Fatigue. Any Fatigue beyond 200 is converted to HP Damage with a Fatigue * 2% chance. For example, a unit with 100 Fatigue who takes 225 Fatigue in a single burst ends up with 200 Fatigue, with a 50-50 chance to lose either 4 or 5 HP.
  • For Communion or Sabbath Slaves, every spell they help cast when already at 200 Fatigue makes them lose 1 HP. This is on top of the standard chance of damage.

1 point of Fatigue is removed from each unit every combat round. Unconscious units lose 5 points of Fatigue instead. Units with points of Reinvigoration lose that much more Fatigue each round.

Drain Damage saps energy from the target and removes Fatigue from the attacker/spellcaster, equal to twice the damage done. Note that most Drain Damage from weapons is "partial", limited to removing only 10 Fatigue at most.