Fatigue

Spending too long without rest results in tiredness, fatigue, which negatively affects the creature's luck.
==Mechanics==
The game manuals claim that characters have a different base fatigue value depending on their constitution, ranging from 4 at con 1, to -5 at con 24, but that's not true, as all player characters have a base value of 0 (though CON does have some fatigue-related effect: see the following paragraphs for an explanation). Player characters start to get -1 luck penalty at fatigue 7 (as shown in FATIGMOD.2da) and that increase up to -94 luck at 100 fatigue. Fatigue can only be decreased by resting or items (Blazing Glory ; The Gift ; Battle Tankard ; Hexxat's Amulet) and Wish: Rest.
Once again, despite what the game manuals claim, every character has a base fatigue value of 0, regardless of their CON attribute. This is the reason why both a character with CON 3 and CON 25 become tired after two Haste casts expire (or with a single cast of a Restoration spell or a combination of reverting the Slayer transformation and a Haste spell expiring, for example) and the save game-editing tool EEKeeper confirms this, as it shows that all player characters have a fatigue value of 0 after sleep (so no negative values).
However, CON does affect how fast naturally-accumulated fatigue (ie fatigue you get over time without sleep) increases, so a character with CON 3 will still get tired much sooner than a character with CON 25 over the course of travels and normal play time, despite having the same initial fatigue value.
The natural fatigue-inflicting effect works in a strange way, because characters don't exactly get fatigue over time in a gradual way; instead, a character will suddenly get 7 or 8 fatigue instantly after a set amount of time (y using EEKeeper and constant saving after 4 hours of travel, one can easily check that the previously-thought relation of 1 fatigue for each 4 hours isn't exactly true). And, with that in mind, characters with low CON values will get a sudden 7 or 8 fatigue penalty suddenly after a set amount of hours pass and higher CON characters will get that same penalty suddenly as well, but only when a larger set amount of hours pass.
==Causes==
* In-game time spent
* Haste spell: +4 fatigue (all affected characters)
* Lesser Restoration, Greater Restoration spell: +7 fatigue (caster only, not target)
* Slayer Form:+4 fatigue after transforming back into normal form
==Gameplay==
* Kicking party members from the group sets their fatigue to base, even if you invite them right back into the party.
* Reloading the game resets accumulated Fatigue (but not the accumulated luck penalty due to Fatigue)
* Battle Tankard makes the wearer immune to fatigue
== Mod Content ==
* The Gibberlings Three (G3) Spell Revisions Mod 5th Level Arcane Spell Waves of Fatigue applies fatigue to creatures in a 30 foot radius Area of Effect - Surges of negative energy render all hostile living creatures in the spell’s area fatigued, as if they haven’t rested in a day. Multiple castings of this spell are cumulative.
== Sources & references ==
* Demivrgvs’s post on BD forum
* semiticgoddess’s post on BD forum