Photo credit via Merriam Webster
Psychologists often treat patients who have mercurial personalities.
Definition
(adjective)
Changing often, or characterized by rapid and unpredictable changeableness of mood. It can also mean having qualities of eloquence, ingenuity, or thievishness attributed to the god Mercury or to the influence of the planet Mercury.
Sentence
Psychologists often treat patients who have mercurial personalities.