(Directed by Alfred Hitchcock.)
Set in a psychiatric institution, where some things are very wrong. A man arrives as a new doctor, but isn't who he seems, and is suffering from some mental problems. While being assessed, he describes a dream that he had, and we see some rather bizarre surreal imagery (created with the aid of Salvidor Dali), as he narrates it to his analyst.
(Note: It's been ages since I've seen this film.)