Alice Klieg (Kristen Wiig), a single woman with Borderline Personality Disorder, is living on disability benefits and lip- synching along to self-improving infomercials and episodes of Oprah when she wins the California Stack Sweepstakes lottery jackpot of $86 million.

The largesse of that amount is more than matched by the largesse of her mental instability and, soon enough, she is writing $15million cheques to fund 100 live-broadcasts of a vanity TV project titled Welcome to Me.

Mostly the show consists of sugar-free recipes (432 calorie meatloaf-cake with sweet potato icing because “sugar addiction is worse than child abuse”), mood-swings and re-enactments of childhood disappointments: a segment called “Someone has been tampering with my make-up bag” ends in cathartic sobbing: “I cried for so many days!”

At first, infomercial star Gabe (Bentley) and his opportunistic brother Rich (Marsden) are happy to take Alice’s money, but as the show becomes increasingly unhinged – not to mention litigious – higher-minded associates like Deb (Cusack) and Dawn (Jason Leigh) become concerned.

This car-crash TV show is the centrepiece for this toe-curling comedy. Wiig’s depiction of a woman whose stories are apt to end with the declaration “then I went off my meds” is as disquieting as it is scarily accurate. Alice’s mental illness coalesces into a distorted echo of social-media “existence”, replete with playground scraps, disproportionate response and absolutely no filters.

She is first introduced in front of a TV that hasn't been switched off in 11 years, surrounded by tapes and books of the mind-body-spirit genre: the room is literally a prison constructed with snake-oil and self-absorption. Bizarre real-life infomercials promise "all of the joy and none of the mess of a real parakeet". Repeated appearances by fake swans add to the sense that Welcome to Me is, in common with its heroine, oscillating as wildly between authenticity and unreality.

Watch between fingers.