“What if there’s no such thing as happiness, only moments of not being depressed?” So asks Jane, the paranoid schizophrenic heroine of “Eternal Beauty,” and it’s one of the more thought-provoking lines in Craig Roberts’ earnest but ungainly sophomore feature — a film that itself stumbles upon moments of clarity without ever finding a happy or consistent groove. Making a comedy about mental illness is a tall enough order without the tricky tonal embellishments, filched from influences as disparate as Paul Thomas Anderson and Terry Gilliam, that Roberts has attempted on an otherwise slender script. With an assist from Sally Hawkins’ valiantly committed lead performance, the result occasionally summons the genuinely disoriented perspective of an unstable protagonist, but more often, it’s the filmmaking that seems to spiral out of control.

Despite an impressive best-of-British ensemble that, besides Hawkins’ go-for-broke star turn, includes support from David Thewlis, Billie Piper, Alice Lowe, Morfydd Clark and Penelope Wilton, “Eternal Beauty” has maintained a low profile since premiering quietly at last year’s London Film Festival: It finally gets a multiplatform release in the UK and North America this week. That low-key presence (for a distinctly high-key film) should be a clue that “Eternal Beauty” is an acquired taste, and one that not even fans of the ample talent involved can count on finding. Still, even bewildered viewers may appreciate its odd, empathetic attempt to engage with a condition too often simplified or vilified on screen.

Explaining her paranoid schizophrenia to a bemused acquaintance, Jane offers this droll observation: “It means I think you’re out to kill me, as opposed to schizophrenic, where I’d be out to kill you.” She’s not averse to making wry jokes about her illness. It’s the best way to deflect the abuse she’s obviously received in spades since being diagnosed in her early twenties, after being ditched at the altar and retreating into an incoherent state of trauma.

Extensive, unenlightened electroshock therapy has left her a frail, shambling ghost of her former self — a point that actor-turned-director Roberts (best known for his lead turn in Richard Ayoade’s “Submarine”) underlines by having “Saint Maud” star Clark play the younger Jane in multiple flashbacks. The physical contrast between Clark’s green, tulip-like rigidity and Hawkins’ transformatively gnarled, stooped body language and teeth-chattering, almost self-echoing delivery couldn’t be more pronounced.

But sanity is a relative concept in this strange, distorted pocket of British suburbia, in which even the period is hard to identify — thanks to the smeary pastels of Kit Fraser’s lensing (shot on Kodak film that gives every appearance of having yellowed and warped with age) and Tim Dickel’s grimy-kitsch midcentury production design. It’s hard to tell from scene to scene if we’re in the real world that drove Jane to the edge, or simply in her off-kilter vision of it.

Either way, hardly anybody in it seems altogether together. Her mother (Wilton) is portrayed as a vindictive shrew who may or may not have imagined a terminal illness, her father (Robert Pugh) seems stunned into catatonic submission, while the younger of her two sisters, Nicola (Piper), is a spiteful gold-digger determined to ape Jane’s schizophrenic symptoms for welfare benefits. Does the act mask mental health issues of her own? Most likely. Only Jane’s kindly, patient older sister Alice (ensemble standout Lowe) might pass for “normal” in this glumly topsy-turvy world — though as she counsels Jane, “You don’t want to be normal, it’s hard work.”

Lowe’s gentle, attentive underplaying is a lifeline of humanity in a film that goes big on loud, freewheeling affectation, both in performance style and formal gimmickry. Jane’s irregular episodes and breakdowns trigger cacophonous surges in score and sound design, along with a succession of variable sight gags — some of which seem plausibly conjured by an unraveled mind, and some of which (in particular macabre series of visions at a Halloween party) play more as forced directorial quirk.

Roberts’ original screenplay, meanwhile, doesn’t offer quite enough character detail or progression to hold this intermittently striking jumble of visual, sonic and atmospheric ideas together. Midway through, Jane’s trudging progress through life is disrupted by a sweet soul connection with fellow psychiatric patient Mike (a porkpie-hatted David Thewlis, exuding a ratty boho charm), and a flare of coy misfit romance suddenly lifts the film into another dimension — until it doesn’t, and a lentil-soupy depressive fog descends once more. There’s something honest here about the way mental health doesn’t follow a clean dramatic arc of betterment and catharsis. Yet even that eventually feels obscured in the juggling labors of a film too eager to amuse, rather than simply observe.