Especially a doctor on whom many lives are depending, because so many of those lives are being lost to fatigue-induced mistakes. I know someone who almost died that way; she had a healthy distrust of hospitals, watched carefully what was going on, and noticed just in time when an exhausted doctor was about to give her the wrong injection which would probably have killed her. The doctor just mumbled "oh, sorry," and shambled on her way, perhaps to kill some other patient at a later date.