I first saw Rodney Ascher’s deeply unsettling sleep paralysis documentary The Nightmare at Sundance in 2015. It may be possible that my mind has erroneously collapsed all of this into one utterly spook-tacular 24-hour time period, but my recollection is that I saw The Nightmare on the same day I also saw It Follows and The Witch. That night, I remember laying awake, prostrate on the floor in my brother’s empty condo, watching shadows crawl up and down the walls as I tried not to run outside screaming headlong into a snowdrift. I was 32.

At the time I probably would’ve pegged the [still-excellent] It Follows as the scariest of the three, and The Witch [ditto] as its most purely and effectively cinematic. I’d been an enormous fan of Room 237, Ascher’s hypnotic feature-length video essay deconstruction of The Shining, which I’d seen at its Sundance premiere just three years prior. And initially, The Nightmare seemed like that film’s somewhat lesser follow-up. Sort like the Pinkerton to Room 237’s Blue Album.

But The Nightmare has only grown in my estimation during the intervening years; a steady ascension that at present moment has it placed it above not just Room 237, but above It Follows and The Witch as well. What makes The Nightmare so scary, you ask? Simple: this movie has the potential to literally kill you.

If you haven’t seen it, The Nightmare is ostensibly a documentary about the odd phenomenon of sleep paralysis. Sleep paralysis [as defined by WebMD] is “a feeling of being conscious but unable to move”—which, given the evidence presented here, is sort of like describing North Korea as “one-half of a peninsula.”

As depicted by Ascher’s vivid recreations—culled from interviews with a half-dozen disparate, articulate, sallow-faced SP sufferers—victims are rendered frozen in their beds, totally locked inside their bodies as visions of terrifying shadow monsters, space aliens, demonic cats, and other fantastical tormentors enter the bedroom to vex and bedevil them.

The condition can even turn deadly—one fatal case was even the inspiration behind A Nightmare on Elm Street. Furthermore, it’s suspected that sleep paralysis may, in fact, be the true root cause in a myriad of alien abduction and haunting stories; a simple quirk of brain chemistry resulting in a tactile, unexplained episode of pain and terror that, for the sufferer, is experienced as completely physically real.

But that’s not even the truly scary part. The truly scary part is that this shit can be contagious. That’s right: the films posits that it’s possible to acquire sleep paralysis simply by knowing that it exists—like something straight out of Chuck Palahnuik’s Lullaby. Thankfully, things have never gotten quite that dire in my own personal relationship with The Nightmare. I can’t claim to have ever suffered from sleep paralysis—either before seeing the film or in the years since—but Ascher’s documentary has played a large role in the development of my own theories around unexplained phenomena and metaphysics.

I don’t necessarily believe in ghosts or aliens or angels. But I do honestly believe that there’s some sort of imperceptible energy field out there; a “world built on top of our world,” to use the parlance of Jeff Nichols’ excellent metaphysical 2016 sci-fi drama Midnight Special. I believe this separate phase dimension exists concurrent to our experience of the “real” world, and that it interacts with our ooey-gooey human brains in a very real, tangible way.

I believe this energy field—let’s call it “Carl”—reacts with people’s brains in all sorts of weird ways to create a variety of odd psychedelic experiences, as filtered through whatever iconographies lurk most significantly in our subconscious: extraterrestrials, poltergeists, religious martyrs, paranoid political fantasies, etc. I believe the existence of Carl will some day be proven scientifically, but that such a discovery won’t necessarily invalidate spiritual belief. It’s also my belief that sleep paralysis, at least as presented by the subjects of The Nightmare, is the closest we’ve yet come to putting our finger on just what Carl actually is. [That, and the familiar—pun intended—feeling of déjà vu that we’ve all experienced at one time or another.]

So really, Rodney Ascher’s The Nightmare isn’t just an informative nonfiction film about a worrisome health issue, or even an effective horror film. It’s also an exploration of the divine. Pretty fucking cool I picked it to be this week’s Cinessential shoot around, huh? Praise Carl, and may your dreams be as blank as the face of numberless clock.