CAROL Morley rushes in and doesn't stop - even when she finally sits still.

Ideas, sentences, thoughts, they all tumble out pell-mell. Some of them dangle half-finished as one of Britain's brightest new(ish) film directors veers off and jumps tracks to start another one.

Sitting in the bar of Glasgow's Malmaison hotel, the woman behind the acclaimed documentary Dreams Of A Life rattles from subject to subject. Morley - the director behind the acclaimed documentary Dreams Of A Life - talks about teenagehood, about her love of Altered Images (the only connection to Glasgow that she can think of), about the films she's made and the films she never got to make. Oh, and mania. Or manias. Which happens to be the subject of her new film.

The Falling - a story of 1960s schoolgirls who succumb to an epidemic of fainting fits, starring Maxine Peake and luminous new talents Florence Pugh and Maisie (Game Of Thrones) Williams - plays out in an opiate haze rather than an amphetamine rush. With the exception of its use of flash edits now and then, it's a dreamy, dark, slow burn of a movie that will either tantalise or horrify.

Because it does, it should be said, go to some very dark places.

In her research for The Falling, Morley discovered that mass hysteria - or mass psycho-genic illness; call it what you will - tends to often happen in schools and tends to happen more often in single-sex schools and most often involves girls and women, "perhaps," Morley says, "because they communicate their symptoms more - if you go along with the idea that that's how they're caused.

"A lot of the ones I looked at from the 1960s were about sexual anxiety so I thought, 'Oh that's great. Let's look at young female adolescents and burgeoning sexuality in the light of changing ideas of sexual morality for women'."

Actually the film goes further, into sexually transgressive areas. As a result it becomes an uncomfortable watch. "I would never want to leave somebody in darkness," Morley says when I bring it up. "I am attracted to darkness but in a way that's not dreary and it's not going to overwhelm you into feeling miserable. I'm not into miserablism, but I am into looking at difficult things in life and trying to throw light on them. We all live with certain things - mental illness and all those things that get buried in life and I think it is important to examine them. But I do want hope for the audience."

The Falling is Morley's first full-length attempt at making a drama. She's already known for her documentaries, most notably The Alcohol Years, a lacerating mirror-image biopic in which she went back to Manchester, where she spent her wild teenage years, to ask the people she knew back then (including the late Factory Records supremo Tony Wilson and Buzzcocks front man Pete Shelley) what she was like, and the aforementioned Dreams Of A Life, her investigation into the life and lonely death of Joyce Carol Vincent, a seemingly gregarious, popular woman who lay dead and undiscovered in her flat for almost three years (played in the film by actor Zawe Ashton).

The real-life origins of both films give them an edge and a painful potency. Now Morley has to show she can mine similar depths within drama.

If anything, she says, making a fiction film is easier than a documentary. "With the documentary work I've done I feel so indebted to the real person." She pauses, qualifies. "Not indebted, but I just want to support them. I found that quite stressful whereas with a drama everyone's acting and everybody's up for it so I enjoy it more."

She has the usual grumbles about filmmaking in Britain. Not enough time. Not enough money. But the experience of being on-set was "fantastic", she says. "I felt very privileged and I didn't want to waste that opportunity."

I remind her of the late Bob Hoskins's moan about his one attempt at directing a film rather than acting in them; that he couldn't get any peace even in the toilet without someone coming up, knocking the door and asking him to make a decision.

She laughs but says, really, it's not about being the big boss. "For me it's not about ego. It's about collaboration and trying to get everybody on the same team so that everybody feels really excited about making this film."

It's an idea that is endorsed when I speak to Tracey Thorn, who has written the soundtrack for the film. "Carol was incredibly hands-off. When she asked me I said, 'Look, I've never done a soundtrack. It's slightly terrifying. I don't really know where to start.' And she said, 'Brilliant. That's even better.'

Thorn was already a fan of Morley's work. "I think there's a real uniqueness and sense of one person's vision. They're very personal films really. The Alcohol Years literally delves into her own past. I know a lot of the people in that film because we're of a similar generation so it's like a record of that time."

It's a record, too, of the girl Morley was between the age of 16 and 21 before escaping to London and art school; a girl who was drinking too much, sleeping around. Someone who could have qualified as that late-1980s media trope, the wild child, if she had been called Amanda or Tamara and been born with rich parents.

"With The Alcohol Years it struck me that a teenager is really anxious about how they appear," Morley says now. "You're very anxious about so much. Looking back, in some ways I wish I could have locked up who I was then so I didn't go through all that. It was funny working with the teenagers in The Falling. All of them, they're so together. I'd just think, 'God, I was so not together like this.'"

Morley was born in Stockport, the younger sister of music journalist and broadcaster Paul Morley. And when she was just 11 years old her father committed suicide. The temptation is to link her wild teenage life with that blunt, hard, overwhelming fact.

But such pop psychology maybe fails to take into account the disorientating strangeness of adolescence itself. "I think so," Morley says. "It's a very complex time. Making The Falling I really wanted to respect girlhood and teenage adolescence and show it as the complex thing it is. Because you are interested in sex and that can often be quite complicated. But I also wanted to show the girls as complex and into ideas and not just into boys, but into so many things because your mind is open. You want to explore. I wanted to look at that."

She pulls back, refocuses on her own back story. "And when you're young, like with my dad, you can be confronted with very difficult situations and you haven't necessarily got any history to cope with that."

She's reluctant in her own life and her films to "get into that thing of, 'well because this happened, that happened'". Because as she says, it's very reductive.

But I'm really good at crass reductions, I tell her. So here's my theory about Carol Morley and her films. They're all about wanting to fit in while not fitting in. "Probably. My assumption is that most people don't really feel they quite belong. And this is why social media has taken off and been so reassuring. It gives people a shape to how they publish their lives and how they fit in. But actually I think most of us always feel ... When you're a teenager you think when you get older at a certain age you'll feel like you've arrived. But you never do."

Really? Doesn't she feel like she fits in within the British film industry? "No. I sort of feel like an imposter in a way. It's amazing to have had backing from the BBC and the BFI but I couldn't imagine someone picking me to direct something."

She stands out of course - depressingly so - because she's one of the few women directors we have in this country (Andrea Arnold and Lynne Ramsay also spring to mind). It is a ridiculously male-dominated industry. "I always like to remind people that only seven per cent of directors worldwide are women. It's even less for directors of photography. I was at some event and I said it's not changed since the beginning of cinema and someone came up to me afterwards and her specialism was silent cinema and she said, 'Carol, actually at the beginning of cinema there were more women making films'."

Great. So we've actually gone back in the last 100 years in this area.

"There's no conspiracy," she continues, "but my analysis of it is that a film needs distribution and certain stories have commercial value and maybe women don't want to tell those stories. So you're going to have a tougher time if you're a writer-director. Once the story is written and the script is going around people are going to go with those with the most experience - I don't blame them - and that will tend to be a male."

Still, she has traction in that world now. Unfortunately we're never going to see her psychological science fiction story Food Farm, based on a Kit Reed short story, or The Trials Of Liz And Alice, about two pole-dancers who go on a tour of the British Isles looking for one of their missing sisters; two projects that she's talked about in the past but which never made it anywhere near a film set. Such is the nature of filmmaking. But there is another project on the cards that will be announced at Cannes this month. An adaptation of a novel by a "major writer".

"I do want to reach wider and wider audiences. I think cinema is for an audience. I know I want to reach a bigger audience and make sure I never become set in my ways."

Carol Morley is not standing still. She doesn't know how.

The Falling goes on general release on Friday

TRACEY THORN ON WRITING THE MUSIC FOR THE FALLING

"Carol said that when she was working on The Falling she had a dream one night in which I did the music for the film. She woke up the next morning thinking, 'Well, why not?' So then she got in touch with me.

"She was excited about the idea of working with someone who didn't completely know what they were doing. So I said maybe I should just approach it the way I normally write, which is just write some songs. Because that's what I do. I don't compose instrumental music.

"So I sent her a song I had written called Let Me In, which has ended up being the final song in the film as the credits roll and she said, 'Bizarrely it just fits, even lyrically.' So it almost seemed there was something fortuitous going on.

"Then she showed me a short scene from the film, the one where the girls are doing the alternative school orchestra. That was the only scene I saw. I wrote two or three little songs and sent them to her and she said 'yes, these are great', and then I watched a rough cut and did some more. So it was done in a really relaxed way. I was just doing what I wanted to do and she took the bits that worked.

"Carol actually sent me the box of the instruments that they play in that orchestra scene. There was a recorder and a triangle and a little xylophone. She said 'why don't you work with these'. So there's almost a sense that maybe the girls have made these songs. They're almost singing their own soundtrack."

An EP, Songs From The Falling by Tracey Thorn, is in stores on April 27.