“Horse Girl” is a candy-colored descent into madness, a lightweight drama that maintains something like suspense as we cringe through a woman’s struggle to just maintain the appearance of “normality” and “sanity.”

Alison Brie of dark comedies such as “The Disaster Artist” and “The Little Hours” co-wrote and stars in this character study in loneliness, sadness and a growing disconnection with reality.

The innocuous title doesn’t give away what a sugar-coated but downbeat movie this is. In the words of the late Vic Ferrari, “Whoa. Hard to get happy after THAT one.”

Brie plays Sarah, a gawky, awkward but cute clerk at the fabric and hobby store, smiling and chatting away her days with her colleagues and her boss (Molly Shannon).

When we see her later at the stables, instructing a wealthy teen in horseback riding, we figure that’s just her side hustle. It’s her birthday, so maybe some other folks from her Zumba class will join her for drinks.

She’s got a roommate, Nikki (Debby Ryan) who has a boyfriend who has a roommate Nikki would like to hook Sarah up with. Nikki even gives her a makeover when the guy (John Reynolds) comes off for drinks — “Show off your body. You never do that!”

All is normal, right down to the conservative late model Volvo Sarah drives around town.

But at home, she sleepwalks. She has nosebleeds. She zones out at traffic lights.

“I’m sorry. I don’t remember!”

She’s absorbed with this supernatural crime drama, “Purgatory,” which features diabolical alien cloning and an intrepid cop (Robin Tunney) out to foil their evil plans.

And she has disturbing dreams, of lying on a white floor alongside strangers, portals of piercing light. Searching the Internet for answers to what ails her serves up plausible solutions, and “alien abduction.”

That’s when she sees a stranger (John Ortiz) from her dreams, a plumbing contractor. That’s when we start to fear for Sarah, worrying that her grip on reality is — like her car — something she will misplace or forget.

That’s when we notice how the other folks at the stables (Toby Huss) regard her warily. There’s a sense of indulgence in the roomie, whose patience is wearing thin, in her kindly boss and in Gary (Paul Reiser), who turns out to be her one-time step-dad.

There’s backstory and “history” coming, and it won’t be happy go lucky.

Brie lays it all out there for this film, struggling to take us inside Sarah’s madness. She has pleasant, sentient moments and manages to clumsily flirt and carry on normal conversations –embellished with tiny fibs and white lies.

Sarah is carrying some heavy secrets.

The tension Brie builds into this character — that Kristen Wiig vulnerability teetering on the edge of pathos thing — and into the story isn’t something easily achieved. “Horse Girl” takes on a dread that grows more disquieting as the movie meanders on.

But that meandering is a problem, the bubbly surface to the character stands out more than the alarm, panic at what she doesn’t understand and more importantly doesn’t remember.

“Horse Girl” makes a nice showcase for a writer/actress with range and fearlessness. It’s just that — dread aside — the film feels lightweight and frothy, first scene to last. She’s put her all into a character that keeps us at arm’s length and a movie that’s not serious enough for its subject — mental illness.

MPAA Rating: R (for language and some sexuality, graphic nudity and drug use)

Cast: Alison Brie, Molly Shannon, Debby Ryan, John Reynolds, John Ortiz and Paul Reiser

Credits: Directed by Jeff Baena, script by Jeff Baena and Alison Brie. A Netflix release.

Running time: 1:44