If you enjoy truly disturbing and mind-warping films, check out Robert Altman's 1972 film Images. It's an often horrific study of a children's author (played by Susannah York) and her rapid descent into genuine schizophrenia and paranoia.
The movie is just amazing, beautifully shot and directed to keep you off-balance. It also features a very interesting, pre-Star Wars score by John Williams.
Images is available on MGM DVD for about 10 bucks and should be seen by any and all fans of serious psychological horror.
Running Time: 101 minutes
Director: Robert Altman
Cinematographer: Vilmos Zsigmond (who was later director of photography for Close Encounters of the Third Kind)
Writers: Robert Altman, Susannah York
Susannah York: Cathryn
Rene Auberjonois: Hugh
Marcel Bozzuffi: Rene
Hugh Millais: Marcel
Cathryn Harrison: Susannah
John Morley: Old Man