Fatigue

Definitions

Physical or mental exhaustion that reduces attention, energy, and decision quality. In technical work fatigue is dangerous because it makes even routine tasks error-prone while often being treated as normal background operating condition.
In plain English: Mental or physical exhaustion that lowers energy and performance.
Example: "The on-call rotation was redesigned after several near-misses made it obvious that fatigue had become a hidden reliability risk, not just a morale issue."