[1] In the United States, the film received a DVD release through Universal Pictures in an eight-film set titled The Hammer Horror Series on 6 September 2005.

[7] On 28 June 2021 Nightmare was released in Europe as part of Powerhouse Films' Hammer Volume Six: Night Shadows limited edition Blu-ray box set.

[8] The Monthly Film Bulletin wrote: "Hammer Mark II, i.e the quasi-Diaboliques exercise as opposed to the Transylvanian blood-bath, has become as rigidly formalised as Perry Mason.

While this makes things easier than ever for horror addicts, it has evidently proved an increasing burden of late for the writer, Jimmy Sangster, in his efforts to find even the slightest variations.

Nightmare's equipage could hardly be more predictable: distraught heroine in ill-lit country house; phantoms gliding upstairs and down corridors; chauffeur, housekeeper, preoccupied and often-absent guardian, enigmatic mistress; knives, turning door-handles, masks, a perambulatory "corpse".

Apart from David Knight, an even less impressive Hammer recruit than Oliver Reed, the players are very sound, Moira Redmond in particular having a field-day with the initially charming, ultimately crazed Grace Maddox.