A not-uncommon condition in which awakening sufferers are conscious but unable to move, sometimes while experiencing fearsome hallucinations, sleep paralysis is natural fodder for horror movies. Its treatment so far has been uninspired, with the partial exception of director Rodney Ascher’s 2015 “The Nightmare,” a semi-documentary in which real-life patients were interviewed, and their waking dreams limned by actors. The phenomenon itself has existed throughout recorded history, inevitably tempting supernatural explanations — a leap that’s easy to fathom, since so many of the afflicted report being menaced in their altered state by ghostly “shadow men.”
Purportedly “inspired by real accounts,” as an opening text duly informs, “Slumber” looks for a while like an above-average treatment of the subject in genre terms. Director/co-writer Jonathan Hopkins sets his tale primarily in the milieu of medical sleep-disorder research, imbuing that environment with a chilly unease, while a cast led by executive producer Maggie Q treats the scenario with admirable seriousness and naturalism. Eventually, however, a promising buildup is eroded by too many rote jump scares, leading to a conventionally hectic and silly climax further undermined by an inappropriately campy, late-arriving performance.
Dr. Alice Arnolds (Q) is an expert in the field of sleep infirmities, working at an institution dedicated to their study and treatment. She didn’t arrive at this speciality by accident — as a child she witnessed her brother’s death while sleepwalking, purportedly under the influence of a malevolent “imaginary friend.” Now she has an occasionally sleep-troubled young daughter to worry about, as well as her own episodes of nightmare and somnambulation. Nonetheless, she regards all such conditions with scientific rationality, believing they can be cured through medical means.
Arriving at the institute in desperate need are the Morgans (Kristen Bush, Sam Troughton), a working-class couple who’ve recently lost one child in a fatal sleep-related accident, and are concerned about their remaining two — particularly Danny (Lucas Bond). The latter suffers terrifying nocturnal visits from some presumably imagined monster while awake that paralyzes him in bed. What’s more, during these episodes, all the other family members experience terrifying dreams that have them sleepwalking (and -talking) around the house, oblivious to Danny’s ordeal. The others’ fits are also disturbing, as mom, dad and sis (Honor Kneafsey) unknowingly perform acts that might bring harm to themselves or each other.
In the facility’s sleep lab, amid a battery of measuring and surveillance devices, the Morgans again enact their bizarre nightly ritual. When Mr. Morgan, in his unconscious state, attacks Dr. Arnolds, it seems the explanation to all their woes is simply a violently abusive parent. But that hypothesis proves false when the phenomena continues back at home while dad haplessly sits in jail.
Soon everyone begins weighing the possibility that an ancient demon might be the culprit; this leads to action that increasingly resembles a rote rehash of “The Amityville Horror” and “The Exorcist,” without the benefit of those films’ more spectacular effects.
Even that underwhelming, derivative turn in Richard Hobley and the director’s screenplay wouldn’t play quite so poorly if not for a ruinous casting decision. Veteran Scottish thesp Sylvester McCoy, a onetime “Dr. Who” more recently familiar from the “Hobbit” films, arrives late in the film to essay the dotty grandfather of an institute janitor (Vincent Andriano), both of whom turn out to have personal experience with the demon in question. The part seems written to be a bit “wacky,” but McCoy’s scenery-chewing ham — offering a characterization somewhere between Truman Capote mimicry and Madame Arcati in “Blithe Spirit” — completely undermines a movie that really didn’t need comic relief. Delighted with himself in a way few viewers are likely to share, McCoy is the wrecking ball that all but destroys Hopkins’ carefully built atmospherics.
The misstep is particularly galling since the other actors work so hard to remain emotionally grounded, from Q’s credibly authoritative, stressed-out lead to the well-handled child performers. Likewise, the physical production is nicely turned even when the script begins to let things down: There’s a sleek, spare, somewhat cold look to the production design and Polly Morgan’s widescreen lensing that builds an effective sense of dread. “Slumber” is ultimately forgettable, but its virtues of assembly and handling are enough to suggest that Hopkins (a veteran of shorts and commercials making his feature directorial bow) could rise to the occasion if given better material.