If I understood it correctly there are currently two systems regarding tiredness. One is the sleep cycle that leads to a tired/dead tired/exhausted state when neclecting sleep and the second system is handing out increasing pain when moving around while overburdened. However there does not seem to be a mechanic that handles short term fatigue while for example fighting.
So one can hold a bottleneck like a window against hundreds of Zs without breaking a sweat while in reality sooner or later exhaustion would kick in and lead to a momentarily decrease of effectiveness. I don’t know if anything is planned for having a sprint option one day but for that a short term stamina system would be attractive too.
My suggestion is to have such a stamina system parallel to the sleep cycle. Exhausting actions like fighting(fighting skill based), hauling(str), butchering(survival) or chopping wood(fabrication?) would temporarily put one into (differently colored) tired, dead tired or exhausted status. Taking a break would get one back into normal with sitting down on chairs being more effective than just standing around. Over the course of a day it also impacts how often one puts himself into the tired state to determine overall sleep cycle tiredness. So chopping wood all day would lead to an earlier general tiredness and longer natural sleep than just reading books or watching water/coal cook.
