Fatigue
Fatigue was a feeling of tiredness, which when symptomatic of an illness, can be either chronic or sudden, and cannot be resolved with rest or sleep.

In 2266, Doctor McCoy asked Captain James T. Kirk to allow him to enter Lieutenant Dave Bailey's insubordination in his medical records as simple fatigue. When Kirk refused, McCoy asserted that the captain overworked him and that he would challenge his decision and claim that he warned him. ()

In 2267, the Talosians interrupted their transmission of events from 13 years before because Christopher Pike was fatigued. ()

According to McCoy's log, Kirk showed signs of  and fatigue just prior to his visit to the Shore Leave Planet. ()

Later that year, Khan Noonien Singh twice claimed to be fatigued to avoid answering difficult questions. ()
 
One of the symptoms of Lewis Zimmerman's terminal illness was fatigue. ()

A spider cow suckled the moisture out of Ensign Brad Boimler which eventually caused it to become fatigued. ()

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Medical conditions