Nightmare (1956)

Stan Grayson (Kevin McCarthy) dreams that he stabs an unknown man to death, but when he awakens, he is disturbed to find that he has bruises that he doesn't remember getting and a key in his room that doesn't belong to him. Confused, Stan explains his situation to his police officer brother-in-law, Rene (Edward G. Robinson), who initially believes that Stan is simply suffering from anxiety. As the evidence continues to mount, however, it seems to point to something more sinister.