Sleep is supposed to be the great surrender. We close our eyes, relinquish control and allow consciousness to dissolve into whatever strange machinery waits on the other side. Horror has long understood the vulnerability of that state, from the nightmare logic of A Nightmare on Elm Street to the psychological labyrinths of contemporary supernatural cinema. Parasomnia takes that familiar anxiety and gives it a promising contemporary framework: what happens when the thing haunting your dreams stops respecting the border between sleep and waking life?

Directed by James Ross II, the Shudder Original places Jasmine Mathews’ Riley at the centre of a story shaped by night terrors, unresolved trauma and disappearance. When her best friend becomes the latest person to vanish, Riley begins to suspect that the demonic presence stalking her dreams may have found a way into the waking world. It is an immediately attractive premise, one that offers the possibility of psychological horror, supernatural mystery and nightmare imagery existing simultaneously, with Riley’s own fractured perception leaving us uncertain about where one state ends and another begins.

Unfortunately, Parasomnia never quite manages to turn that intriguing foundation into the film it initially promises to be.

There is plenty here to admire. The central concept has genuine potential, particularly in the way it connects Riley’s trauma with the supernatural threat. Rather than simply introducing a demon and allowing it to run amok, the film attempts to make the creature part of a larger psychological landscape. Riley’s night terrors are not merely convenient vehicles for scares; they are connected to grief, memory and the unresolved events that have shaped her life. That gives the supernatural elements an emotional foundation, even if the eventual story struggles to build upon it.

Jasmine Mathews is particularly strong in the lead. Riley could easily have become a conventional horror protagonist — traumatised, frightened and increasingly convinced that nobody believes her — but Mathews gives the character a more complicated interior life. There is a convincing fragility to her performance, but also a determination that prevents Riley from becoming passive. She carries the film through some of its weaker narrative stretches, grounding the more fantastical material in recognisable human emotion.

That becomes increasingly important as the storyline begins to show its limitations.

The problem with a horror film built around dreams is that the possibilities are virtually limitless. Once the audience understands that reality itself may be unreliable, the filmmaker has access to a wonderfully unstable cinematic space. A bedroom can become a trap. A familiar face can become threatening. A mundane location can suddenly acquire the logic of a nightmare. The rules of reality can be stretched, distorted or discarded entirely.

Parasomnia occasionally understands this, but too often it seems reluctant to fully embrace the possibilities of its own premise.

The film’s strongest moments are those in which uncertainty takes precedence over explanation. When Riley is caught between sleep and waking, the question isn’t necessarily whether what she is experiencing is real, but whether reality still provides a useful distinction. Those sequences possess an unnerving ambiguity, allowing the horror to operate somewhere between psychological breakdown and supernatural intrusion.

Yet the more the film attempts to explain its mythology, the less compelling that ambiguity becomes.

This is a recurring problem with supernatural horror. The unknown is often considerably more frightening than the known, particularly when the unknown exists inside something as personal and uncontrollable as a nightmare. Once the film begins establishing the mechanics behind its demonic presence, some of the mystery starts to evaporate. The audience is no longer trapped inside Riley’s uncertainty; we are increasingly being given the answers.

And unfortunately, those answers aren’t always particularly satisfying.

The storyline feels serviceable rather than revelatory. There are ideas here that could have produced something considerably more psychologically intricate, particularly around trauma and the persistence of grief, but the screenplay frequently settles for conventional supernatural-horror machinery. Characters move towards revelations because the narrative requires them to, discoveries arrive with an increasingly familiar rhythm and the mystery ultimately feels less substantial than the concept that initially introduced it.

This is where Parasomnia becomes frustrating rather than outright disappointing.

Because there is clearly a better film lurking inside it.

The concept is strong. The performances are strong. The atmosphere is often effective. There are moments where the film creates precisely the kind of disorientation it needs, leaving Riley — and the audience — uncertain about whether they are experiencing a nightmare or something considerably more tangible.

But those ingredients don’t quite coalesce into a satisfying whole.

The supernatural entity itself is another example of this imbalance. As an idea, a demonic figure capable of moving between dreams and reality is an excellent horror proposition. It weaponises one of humanity’s most universal vulnerabilities: sleep. There is something deeply unsettling about the possibility that closing your eyes doesn’t protect you from the monster, but actually gives it access to you.

Yet the creature ultimately feels more effective as an idea than as a fully realised antagonist.

The film is strongest when the demon remains at the periphery of Riley’s experience, when its presence is suggested through fragments and disturbances rather than presented as something that needs to be completely understood. Once it becomes a more conventional supernatural threat, Parasomnia loses some of the psychological unease that made its premise so attractive.

There is also a noticeable tension between the film’s ambitions and its storytelling. It wants to explore trauma, grief, friendship and the lingering consequences of tragedy while simultaneously delivering supernatural thrills. Those elements are not incompatible — horror has been doing exactly that for decades — but they require a narrative capable of allowing the emotional and genre components to reinforce one another.

Here, they sometimes feel like separate tracks running alongside each other.

Riley’s emotional history gives the horror meaning, but the horror doesn’t always deepen our understanding of Riley.

That distinction matters.

The best psychological horror makes the monster inseparable from the character confronting it. The supernatural threat becomes an external expression of something internal, allowing every encounter with the creature to reveal something about the protagonist. Parasomnia gestures towards that territory without quite committing to it.

As a result, the film’s emotional material can feel somewhat underdeveloped just when it should be reaching its greatest intensity.

That is particularly evident in the final act.

Without venturing into spoilers, the conclusion struggles to deliver the catharsis that the preceding story seems to be building towards. The film has established a compelling relationship between Riley’s trauma and the supernatural threat, but the eventual resolution doesn’t quite capitalise on that connection. Instead of transforming the earlier ideas into something thematically resonant, the ending largely feels like the narrative arriving at its required destination.

It isn’t disastrous.

It simply isn’t enough.

And that distinction is important because Parasomnia is never a bad film. It is an intermittently effective one that repeatedly demonstrates what it could have been. There are enough strong ideas and performances here to make the experience worthwhile, but also enough conventional storytelling to prevent it from becoming the psychologically disquieting nightmare its premise suggests.

Mathews remains the film’s greatest asset. Her performance gives Riley emotional credibility even when the screenplay becomes predictable, and she brings enough vulnerability and resolve to make the character worth following. The supporting performances similarly help maintain the film’s human dimension, preventing the supernatural material from becoming entirely detached from the people experiencing it.

Ultimately, however, Parasomnia is caught between two versions of itself.

One is a strange, unsettling psychological horror about trauma invading dreams and nightmares crossing into reality. That film is genuinely intriguing. It understands that the most frightening aspect of sleep is not necessarily what we dream about, but the surrender of control that makes dreaming possible in the first place.

The other is a more conventional supernatural thriller that needs to explain its mythology, organise its scares and eventually provide answers.

The first film is considerably more interesting than the second.

When Parasomnia embraces uncertainty, it works. When it allows Riley’s perception to become unstable and makes us question whether the nightmare has crossed over or whether Riley is simply losing her grip on reality, the film finds its unsettling centre. But whenever it retreats into familiar supernatural storytelling, the tension dissipates.

There is a good horror movie buried somewhere within Parasomnia. At times, you can almost see it clawing its way to the surface.

What ultimately holds it back is not a lack of ideas, atmosphere or talent. It is that the story doesn’t quite know what to do with all three.

The Prognosis:

Parasomnia is a film with a genuinely strong horror concept and committed performances, particularly from Jasmine Mathews, but its mediocre storyline prevents the material from reaching its full potential. It is worth entering the nightmare for the atmosphere and ideas; just don’t expect the waking world to provide quite the payoff you’re hoping for.

• Saul Muerte