"Nightmare" (1964) is a Hammer horror/thriller starring: David Knight, Moira Redmond and Jennie Linden.
Janet, a teenager who goes to a private boarding school has some issues. Her mother is in an insane asylum because she stabbed Janet's father. Janet has recurring nightmares of her mother and of herself doing horrible things. She is afraid she has inherited her mother's madness. She leaves school early and returns under the watchful eye of her schoolteacher Mary Lewis to her family home.
Her guardian Henry Baxter has arranged a nurse named Grace Maddox to be there. Shortly after arriving, Janet continues to have dreams that she can't decide are dreams or reality. She also keeps seeing a scar faced woman in white that glides around the house. Poor Janet seems to be going mad, or is she being driven mad?
This film takes an unexpected turn a little over halfway through. This is good, suspenseful thriller that will keep you guessing until the end.