Bipolar personality disorder
Bipolar personality disorder was a medical condition characterized by paranoia.
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. He also recommended that Starling find a psychotherapist. (VOY: "Future's End, Part II")