Diana Lorys is Anna, a nightclub dancer, who meets Cincia (Colette Jack), who invites Anna to her home. Cincia tells Anna that her talent and beauty are above and beyond where she is working and makes a vague promise to Anna that she can make her a bigger success. Anna agrees and soon finds comfort in Cincia's home. A local doctor, Paul (Paul Muller), is eventually summoned to Cincia's home under the assumption that Anna is ill. Apparently, Anna has been having nightmares--those of her killing people or waking up not knowing what she has done, with someone dead in her bedroom. 
Les cauchemars naissent la nuit is, as a mystery, reminiscent of Umberto Lenzi's Orgasmo (Paranoia) (1969) in the respect that Anna's reality is being manipulated by those around her. Anna's subsequent madness is borne from this manipulation. The key figure in this manipulation would have to be Colette Jack's Cincia, but during the nightclub sequence when Cincia first sees Anna, it would appear that Anna actually seduces Cincia. Anna's striptease sequence is shot in Franco-style (aka very lovingly) (aided by José Climent's photography and a sexy score by Bruno Nicolai); and it almost seems that Cincia is compelled to have Anna in her home. 
Lorys's Anna remains the focus of Les cauchemars naissent la nuit, and this makes it difficult to discern what is going on around her. Franco shows many an emotional scene where Anna wants to flee Cincia's home, and Anna often runs into the arms of Muller's Paul. She continually asks for help. Paul, not uncaring, lends a sympathetic ear, yet his ultimate advice is often just "go home and rest." 
More telling perhaps about Les cauchemars naissent la nuit is where this falls in Jess Franco's filmography: it is only slightly removed in time from his previous Eugénie (1970); and his subsequent film would be Christina, princesse de l'érotisme (1971). It is very easy to see Les cauchemars naissent la nuit as an experimental, transitional film: Les cauchemars has the intense subjective sexual obsession of Eugénie combined with the ethereal, almost random, characters of Christina. Jack Taylor appears late in the film as one of Cincia’s lovers; and when Anna and Taylor’s character interact, it is often composed of poetic, playful dialogue. Taylor’s character doesn’t seem real, and if he’s helping Anna, then it is very cryptic. Finally, giving a very precious appearance in a small performance is Soledad Miranda as a beautiful girl peering out of a window across the street from Cincia’s house. She has dreams that she shares with her lover of coming into a lot of money (this is important to the plot?). Miranda is dead sexy--Franco composes her primarily nude wearing only thigh-high boots. Franco had an intense obsession for Miranda, and it undoubtedly shows.
Les cauchemars naissent la nuit is a lithe, meandering, arty, poetic film. I tend to prefer my cinema like this--a film which has really nowhere in particular to go in terms of story, so its imagery becomes prominent and, in the case of Franco, seductive. A minor entry, perhaps, in Franco’s filmography, because of the films preceding and following it. However, here’s some facts to conclude this post taken from essential Obsession: The Films of Jess Franco:Only released in Belgium, this variation of the Miss Muerte story (a nightclub dancer unconsciously commits murders for somebody controlling her) has become virtually invisible since this limited release. Franco used the same story three years later for his own production of Los Ojos Siniestros del Dr. Orlof. Local critics writing about Les cauchemars naissent la nuit found that “the vague screenplay in the crime novel vein was only a pretext for showing scenes of a dubious nature with excessive nudity.” It is also true that Belgium is probably the most prudish country in Europe: even sex magazines are sold with stickers to cover genitalia! When asked (in Vampirella n° 13) what had been his smallest budget to date (in 1973) Franco named this film.
(from Obsession, ed. Lucas Balbo & Peter Blumenstock, Graf Haufen & Frank Trebbin Publishing, Munich, Germany: 1993, p.77)
Les cauchemars naissent la nuit has been released by Media Blasters/Shriek Show on DVD as Nightmares Come at Night. Also, check out Aaron’s review at his killer blog, The Bone Throne.
