Bipolar personality disorder
Bipolar personality disorder was a medical condition characterized by extremes of emotion.

Following Lon Suder's murder of Frank Darwin in 2372, Kes found no tendency towards bipolar disorder in Suder's neurogenetic markers. ()

In 1996, The Doctor told Henry Starling that his belief that the  crew was attempting to steal "his" timeship, because they thought he'd be an easy target, was a paranoid response indicative of bipolar personality disorder. ()

See also
 Mood swing

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Medical conditions