(Beyond travel fatigue, sleeping in armor fatigue or magical fatigue) the rules for getting tired are pretty much not there. You're on your own.
If you'd like some easy to complex house rules you can use these:
After being awake for 24 hours (DMs seeking complexity can use 12 hours plus constitution score instead of 24 hours), you become fatigued.
After 12 more hours (DMs seeking complexity can use the constiution score instead of 12 hours), you become exhausted.
After 12 more hours (DMs seeking complexity can use the constiution score instead of 12 hours), you must make a fort save every hour with a DC of (10 + 1 per prior check) to stay awake. DMs seeking added complexity can impose a d6 temporary wisdom damage (healed upon a full rest) on a saving throw made by 5 or less.