Carol Morley’s entirely absorbing new film is about a mysterious outbreak of mass hysterical fainting at a girls’ school in the late 1960s. The Falling is a non-sci-fi sci-fi, a deadly serious black comedy and a psychological drama in which psychological assessments are beside the point. It comes from the heart of a certain kind of Englishness: as murky, wet and luxurious as the water in which Millais drowned Ophelia. With its superb musical soundtrack by Tracey Thorn, it actually has a seductive prog-rock sensibility, with something of Nick Drake. And in fact this entire deeply strange drama feels like the film version of some giant lost concept album that the late Syd Barrett might have been working on over 20 years in his bedroom.

Maisie Williams – Arya from TV’s Game of Thrones – plays Lydia, a tack-sharp girl who is the best friend of Abbie, played by newcomer Florence Pugh, the prettier and more sexually successful of the two. Abbie reads Wordsworth’s Prelude aloud in English class with a melodramatic verve that her otherwise approving teacher has to rein in, and she is the leading light of the Alternative School Orchestra, which performs chamber-pieces marked by the hypnotic glissando clatter of a xylophone.

But the friendship of Lydia and Abbie is damaged by the fact that Abbie has had sex, and this has consequences. Abbie feels strange – and so, sympathetically, competitively, uncomprehendingly, does Lydia. Abbie confides to Lydia how orgasm is like a “little death”; she is sick in the girls’ toilets and then reveals something even more secret and intimate than pregnancy. From this catastrophe, accelerated in some obscure way by Lydia’s dysfunctional relationship with her agoraphobic mother (Maxine Peake), there is a contagion of group fainting led by Lydia herself: in the classroom, in the art room, outside in the handsome grounds where a colossal oak broods over a lovely pond and even – spectacularly – in the school assembly, when a guest speaker has been invited to address the girls on the appallingly ironic subject of accidents in the home. The headmistress, played by Monica Dolan, is seen to wobble slightly, groping for the lectern.

Part of is it the break between Lydia and Abbie, and the willed end of a friendship, like the dumping of a girlfriend or boyfriend, is one of the great forgotten traumas of teenagerdom. “You’re think we’re over?” demands Lydia of Abbie. This emotional break could be the atom-split which releases strange, occult energy.

Morley has clearly imbibed the eerie enigma of Peter Weir’s 1975 movie Picnic at Hanging Rock, about an Australian schoolgirl party that mysteriously disappears, and also Peter Jackson’s underrated 1994 gem Heavenly Creatures, about the combustible, violent relationship of two teenage girls. There are also echoes of film-makers like Lucrecia Martel and Lucile Hadžihalilović. And occasionally, in all his fervent transgression, this feels like an early short story by Ian McEwan.

But really, The Falling is very distinctive: in its deadpan humour, wan regret and elegant compassion, I think it could only have come from the director of that renowned documentary Dreams of a Life about the lonely death of a single woman in north London. Morley explores the idea that the fainting is all about denied or displaced sexuality, the explanation traditionally offered for hysterical outbreaks – particularly in late 17th-century Salem. The Falling may in fact be based partly on a case in Blackburn in the mid-60s. But the director seems to me to be insisting on something else.

It could be that The Falling is about something other than sexuality or more than sexuality — it could be about the young women’s partial, poignant access to a kind of energy and creativity for which their background and education has not prepared them. One of the incidents happens when they are reading aloud from the New Testament, and it begins to have a dreamy, dance-y, ecstatic quality, a kind of unlicensed bizarre agape festival-cum-mass-nervous-collapse that none present can understand.

Morley tracks the looks and moments and smiles that lead up to the outbreak: the repetitive behaviour, touching your face in a certain way, pulling your blouse to conceal marks on the skin, possibly signs of self-harm. The cross-current of glances and shared, intimate realisations. To balance this, there are some superb moments of demure deadpan comedy: Dolan’s eccentric headmistress, who smokes cigarettes incessantly, brings one of the fainting girls round, by smartly pricking the pin of her brooch into the girl’s thigh.

This is terrific film-making – enough to bring a rush of blood to the head.