In Hypochondriac, the impressive feature debut from writer-director Addison Heimann, Zach Villa plays Will, a young man who seems to be coping remarkably well with the trauma of his mentally ill mother trying to kill him when he was a child. He makes beautiful high-end pottery, offers sweetly funny coping skills to a co-worker who suffers panic attacks, and has a charming, lovable boyfriend of eight months, Luke, played by Devon Graye.

The first fissures in his life appear when Luke asks him, innocently enough, if he’d like to have brunch with him and his mom on Mother’s Day. Luke is sensitive enough to ask if this might be hard for Will, since his mother has been dead for years.

By this point, fairly early in the film, we already adore Will — he’s warm, he’s direct, and Villa has the kind of charisma you build superhero movies around. So it’s wincing to watch his lovely life go to hell, as his coping mechanisms, and numerous medical professionals, fail him horribly.

You may want to skip the rest of this paragraph, which has some spoilers. But the way Hypochondriac most effectively embodies Will’s terror is in the form of a wolf-creature very reminiscent of the rabbit that bedevils Jake Gyllenhaal’s titular character in Donnie Darko. Heimann upends the Don’t Show the Monster rule, instead injecting the monster with increasing frequency, and near-total effectiveness, into increasingly discomfiting scenarios.

Hypochondriac is an unnerving, disorienting and rule-breaking film, and I saw it in maybe the ideal setting: at the very well-programmed Boston Underground Film Festival on Friday at the Brattle Theatre, one of my favorites. It’s a nearly 70-year-old, single-screen rear-projection movie palace that you enter by descending down a stairwell from Cambridge’s Harvard Square. As the posters on the wall, and especially the bathroom, make clear, it loves arthouse and cult horror films equally, and makes you feel every time you visit like you’re entering a secret, giddily nerdy movie club.

Hypochondriac is a great fit. It rewards you for your past film viewing (especially a show-stopping scene in which Will practices his craft), as well as your knowledge of the way these kinds of films are supposed to work. But then it takes aggressively unexpected turns. It was one of those movies where, about four-fifths of the way in, I had absolutely no idea how it would end.

We all know how mental-illness thrillers have historically worked — protagonists gaslit by their own brains are punished for being themselves, essentially. We wonder if the horrors they face are supernatural, or all in their heads, and if the answer is all in their heads, the film often invites us to go home with a smug superiority: I knew it all along. It’s the hero’s fault for being crazy.

Hypochondriac, like 2020’s Horse Girl, breaks from this tradition by having real empathy and hope for its protagonist. Our horror at Will’s situation is all the more acute because Heimann does such a good job, early on, of establishing him as a real person who deserves our care. What he experiences feels like something that someone we love may someday suffer, if we don’t suffer it ourselves.

Villa, previously known for playing Richard Ramirez (pretty much the opposite of Will) in American Horror Story, is someone to watch. He has astonishing range in Hypochondriac, and a less skilled actor would have tanked the film, given its ambitious tonal changes. I’m also jazzed to see what Heimann does next. He deftly handles very tough material, taking big, weird creative risks that pay of exuberantly — especially when our favorite hypochondriac visits a hilariously bro-y nurse practitioner played by Michael Cassidy. (I suspect he, like Villa, will be snatched up for some very big projects very soon.)

The rest of the supporting cast is also strong, including Madeline Zima as a very funny and very terrible potter-influencer, and Marlene Forte as a character I probably shouldn’t say too much about.

Hypochondriac, which played at the Boston Underground Film Festival after debuting at SXSW, has been picked up by XYZ Films for theatrical and home release later this year. For best results, try to see it somewhere as film-mad as The Brattle.