"If I Had Legs I'd Kick You" would qualify as a horror movie if it had a monster lurking somewhere in the protagonist's house instead of inside her head. Writer-director Mary Bronstein's second feature (after a 17-year professional hiatus) has dark Lynchian visual elements and an emotional atmosphere that echoes the nerve-scraping work of the Safdie brothers, both of whom acted in her 2008 debut, "Yeast," and one of whom, Josh Safdie, is a producer here. (In addition, the director's husband, Ronald Bronstein, who cowrote the singular Safdie films "Good Time" and "Uncut Gems," has a voice role in this picture.)

But "If I Had Legs" is distinguished by its own raw originality, and by the ferocious performance of its star, Rose Byrne, long known for mainstream hits like "Bridesmaids" and the "Insidious" films. Here, she rises up to an altogether higher artistic peak.

Byrne plays Linda, a psychotherapist living and working out on the far eastern tip of Long Island, New York. Linda's husband, Charles (Christian Slater, largely unseen), is away a lot for his job, leaving Linda to tend to the many needs of their daughter (Delaney Quinn, almost entirely unseen, although endlessly heard) on her own.

The maddening demands of motherhood have seldom been so harrowingly depicted as they are in this movie. Linda's little girl is afflicted with an unspecified malady that is starving her body of vital nutrients. This necessitates constant intravenous replenishment, which in turn requires Linda to constantly monitor the girl's incessantly beeping transfusion machine. And she's further plagued by her daughter's nonstop whining (she wants a different kind of pizza, she wants to talk to her daddy, she wants a hamster). Linda's life has devolved into a mind-numbing, never-ever-ending routine. And it becomes even more oppressive after the ceiling in her home develops a crack that bursts open and floods the premises, requiring mother and child to relocate to a seedy beachside motel.

Left to her own lonely devices — mainly cheap wine and pot — Linda's personality begins to crater. Her own psychotherapist, an abrasively haughty character (solidly portrayed by Conan O'Brien), is no help. ("Are you listening to me?" she shouts at him. "Can you hear me?") And her own clients — like the creepy kid who tells her about a dream he had in which she kissed him — are largely insufferable. She feels besieged at every turn — by a hostile parking-lot attendant at her daughter's clinic and by the head doctor there (played by Mary Bronstein), who berates her as a substandard caregiver.

Linda's only emotional lifeline is provided by a genial motel neighbor named James (rapper-actor A$AP Rocky), who guides her on a journey through the dark web in search of cocaine (Linda's favorite drug) and molly (James' high of choice). She also takes him out to show him the hole in the ceiling at her home, which remains wide open and untouched by the contractors she's paying to repair it. Then something violent happens, and Linda's life, already a mess, gallops off in the direction of nightmare.

Bronstein fortifies her story with obstetrical and outer-space imagery, and we can feel Linda being drawn into these visions. The director also brings in archival footage of Andrea Yates, a Texas woman who in 2001 drowned her five children and was adjudged to be afflicted with postpartum psychosis. What takes us deepest into Linda's mind, however, is Bronstein's visual strategy of shooting Byrne's face in extreme closeups — showing us every twitch and wrinkle, and her character's every doubt and hesitation. "Time is a series of things to get through," Linda says. Or die trying.

Photos courtesy of A24