As Donald Guarisco writes, “This Hitchcock-inspired blend of mystery and thriller from Hammer Films is gimmicky in the extreme but that’s also part of its charm. Nightmare hinges upon a rather flamboyant narrative from house scripter Jimmy Sangster: some logic loopholes become apparent if you look at his wild plot too closely but he attacks his storyline with great gusto and pulls off a clever, Psycho-derived plot switcheroo that will throw the audience for a loop.
It also helps that Nightmare is directed with great panache by Freddie Francis, who uses John Maxwell’s moody black-and-white photography to tremendously atmospheric effect. Francis creates a number of genuinely intense setpieces along the way, cleverly using his framing choices and editing to comment on the story’s events.
Finally, Nightmare benefits from committed performances by a solid cast: Jennie Linden offers an intense turn as the film’s troubled young heroine and her work is supported nicely by strong turns from Brenda Bruce as a wise, sympathetic teacher and Moira Redmond as a mysterious nurse brought in to watch over Linden. To sum up, Nightmare is an effective little chiller that packs a surprising punch for a film of its age.”