Filmmaker Rodney Ascher’s follow-up to his intriguing 2012 documentary Room 237 delves into similar psychological horror territory but, whereas that film presented an intricate interpretation of Stanley Kubrick’s take on Stephen King’s fictional tale The Shining, The Nightmare concerns itself with the real-world phenomenon of sleep paralysis.

As this documentary reveals, it is a frightening (yet fairly common) condition in which a sufferer will find themselves unable to move and subject to torment from hyper-real, malevolent manifestations – shadow men, aliens, spirits – before awakening to find it’s all been a dream. Through a series of talking-heads and chillingly effective dramatic reconstructions, we see how this affliction has affected several ordinary people, many of whom have suffered this often nightly ordeal since childhood and, as a result, walk a fine emotional line between lucidity and madness.

There’s no denying the personal impact of these extreme nightmares, yet this is the only angle Ascher is interested in exploring and, as the film progresses, it becomes very one-note. The experiences and stories – which have all been gathered from the US and UK – are extremely similar and, while initially frightening, the effect is quickly eroded by repetition.

There is also a total absence of any counterbalance in the form of expert contributions, or scientific and psychological explanations; nothing whatsoever to give this documentary any depth beyond the testimonies presented on screen. Indeed, the only wider context comes when the interviewees briefly recount what they have discovered about their torment on Wikipedia.

While Ascher’s focus is explicitly on the exploration of the power of nightmares on an individual level – his ramping up of the fear factor underscored by a horror movie palette and foreboding score – this narrow approach ultimately undermines what could have been a fascinating investigation into the awesome power of the human psyche.

Selected release from October 9, 2015.

This review was originally published at The List