Shadow and Light (1951)

A world-renowned concert pianist whose favorite composition is Tchaikovsky's Piano Concerto #1 starts to go haywire during one of her concerts, much to the other musicians' dismay, and it's said that her father had lost his mind before he died. A psychiatrist explains to her that she suffers from a neurosis called "narcissism": she sees "reflections" on her piano (and occasionally on mirrors she relegates to the attic), and the face that appears is "the other me"--probably her inflated ego. Perhaps this unfortunate artist would never have had a relapse if she'd been treated by a compassionate therapist. But she falls in love with a handsome sawmill owner--who happens to be her sister's former lover.