Bipolar personality disorder is 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. (VOY: "Meld")
In 1996, The Doctor told Henry Starling that his belief that the USS Voyager 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. (VOY: "Future's End, Part II")