It’s easy to conflate documentary with truth, or more specifically The Truth, with a capital T, as if there were one true and right answer in all things. It can be hard not to, especially when the truth or what passes for it feels so elusive. Cinéma vérité strives to create this for us, its founding principle being to let things unfold as if the camera were not even there, as if the director did not exist. At perhaps the opposite end of the spectrum are filmmakers like Herzog whose personality is so infused in every second of every documentary he makes, it’s impossible to separate him from his subjects. You watch Grizzly Man or Lessons of Darkness acutely aware of his presence and how he feels about what he’s showing you. But even when the director takes a backseat to his subjects, his or her presence can still be felt on screen, it’s just not going to be as obvious.

So where does Rodney Ascher’s 2015 horror-documentary The Nightmare fall on the spectrum? At first glance, it would seem to lean away from more persuasive arguments by putting the entirety of its focus on its subjects: a handful of disparate people suffering (or that have suffered) from sleep paralysis. We listen as they tell their stories while Ascher himself is barely present, save for the one or two questions we hear him ask (largely from off-screen) before disappearing into the background once again.

But in combining documentary with horror, you might think Ascher’s perspective is plain, if not plainly stated. Sleep paralysis terrifies him, and he’s constructed The Nightmare specifically to terrify you, too. The film’s most obvious tactic here is its carefully constructed re-creations of the subjects’ nightmares. Menacing figures stand out against sets lit up in electric reds, blues, and greens giving them a sick circus quality that’s almost disorienting to look at.

But the terror here feels born out of a heightened accuracy, not gimmickry. The faceless shapes are frightening because the dreams were frightening. The lighting and score intensify the scene for us in the hopes of matching the intensity of the fear felt by the subjects. Ascher wants us to understand just how terrifying sleep paralysis really is.

All of this is true. At the same time, his real thesis is almost hidden, because it isn’t expressed by what’s on screen, but what’s conspicuously left off screen.

With all the care Ascher puts into interviewing his subjects, giving them the space to explain their experiences in their own words, he appears to reserve all judgment as to the veracity of their claims. We see this most clearly in the hands-off manner he approaches the various ways they try to make sense of what they’ve gone through. There’s the woman certain one of these instances was the ghost of mother, the methodical young man that believes he’ll suffer from it until it kills him, the woman who thinks it was a dark supernatural force, yet another sure that her recovery from these episodes is proof that God exists.

The film doesn’t argue that any of these people are right or wrong; it merely presents their perspectives without comment. The viewer can then align themselves with whichever person most lines up with what they’re already inclined to believe. You’re free to take from it what you will.

But that’s where the missing piece of the puzzle comes into play: the one thing we never see is an actual expert. Ascher never films an interview with a doctor, sleep specialist, or psychiatrist. The only bits of expertise we get are filtered through the subjects’ own recollections and personal feelings. In leaving this out, Ascher is taking as strong a stance as any amount of Herzogian voice-over could. He’s effectively removing science from the equation and arguing that what really matters is the ambiguity, the lack of certainty, most of the subjects feel.

By focusing on their stories this way, it’s easier to go along with their more haunting explanations for the phenomenon. Ascher even uses CGI re-creations of synapses when some of the people describe the way the paralysis feels. This is a visual cue that reads to an audience as scientific (and thus more true), but there’s nothing scientific about it at all.

It’s because Ascher wants us to walk away without concrete answers, without giving us “the truth” we might expect or want, that The Nightmare can succeed as a horror film. He hurls us into the deep end of the pool, but doesn’t throw us a life preserver to drag ourselves out again. Instead, we have a breadth of options (including religious and supernatural ones) that we’ve been primed to be more susceptible to. As if that weren’t enough, the documentary provides just enough knowledge of sleep paralysis to show viewers what it’s like, while leaving enough ambiguity to its causes that it leaves you wondering one question and one question only: will it happen to me?

Neither Ascher nor the film can answer this for us. It only presses to dread it, and because it is real, so is our fear.