I've always liked the idea of fatigue rules, but they tend to be too complicated and its not worth slowing play down. Its one of those things where my desire for verisimilitude is at odds with my desire for ease of play. Game of Thrones had a fatigue mechanic, but it wasn't great. -1 per round past the threshold or something. It didn't really click with my group.
Here's what I've been batting around, probably since 2e. A character's Con is his Fatigue Score. You'd write it down over by Saves. Light weapons would be 1 fatigue point, normal weapons 2, 2-hand weapons 3 (maybe, I'm not married to the numbers). A round spent attacking with a Light weapon would be 1 Fatigue (just for the attack or full-attack action, not per attack).
A character who surpasses his Fatigue Score becomes Fatigued, and the counter resets. Once he surpasses it again, he becomes Exhausted. For simplicity, I'd say Fatigue disappears at the end of the encounter, and exhaustion takes an hour to go away. (Similar to the barbarian's fatigue after Rage. Also, Fatigue wouldn't kick in until after Rage or Frenzy ends.) Or, Fatigue could be like normal and spells like Lesser Restoration would be more important. (Maybe a 1st level spell like Refresh that removes or downgrades fatigue/exhasution could be used.)
I know, I know, one more thing to keep track of. Believe me, I get that. If I were going to introduce something like this, it would be in a low-level game where there isn't very much to keep track of, to give my group a chance to road test it and get used to it. I've just always liked the idea.
Here's what I've been batting around, probably since 2e. A character's Con is his Fatigue Score. You'd write it down over by Saves. Light weapons would be 1 fatigue point, normal weapons 2, 2-hand weapons 3 (maybe, I'm not married to the numbers). A round spent attacking with a Light weapon would be 1 Fatigue (just for the attack or full-attack action, not per attack).
A character who surpasses his Fatigue Score becomes Fatigued, and the counter resets. Once he surpasses it again, he becomes Exhausted. For simplicity, I'd say Fatigue disappears at the end of the encounter, and exhaustion takes an hour to go away. (Similar to the barbarian's fatigue after Rage. Also, Fatigue wouldn't kick in until after Rage or Frenzy ends.) Or, Fatigue could be like normal and spells like Lesser Restoration would be more important. (Maybe a 1st level spell like Refresh that removes or downgrades fatigue/exhasution could be used.)
I know, I know, one more thing to keep track of. Believe me, I get that. If I were going to introduce something like this, it would be in a low-level game where there isn't very much to keep track of, to give my group a chance to road test it and get used to it. I've just always liked the idea.