Toni Collette is starring in what’s being billed as the most terrifying horror film in years, and she doesn’t even like horror films. Or, rather, she doesn’t know whether she likes them, because she’s too scared to watch them.

We’re discussing how her new film, Hereditary, by first-time director Ari Aster, operates beyond the horror genre, bringing in other psychological dimensions, and I mention how The Shining, one of the major influences pumping through Hereditary (along with Rosemary’s Baby, The Exorcist, and The Babadook) wasn’t just about horror either, when Collette interjects: “I haven’t seen that.” I must have gaped, because she laughs and says: “I don’t like horror films.” She says she bought The Shining DVD years ago but it’s still got its wrapper on. “I’m just too petrified to watch horror films!” But you’re OK about starring in them? “I look for challenging work, and this was so complicated, layered, dense and honest. And unusual. It felt really original, even on the page. That’s what I hope for in life. And it rarely comes along.” Full of praise for Aster (who also wrote the script), Collette accepts that Hereditary is a horror film, “but it isn’t just a horror film. It’s this kind of beautiful fragile story about people living with huge amounts of emotional pain.”

In the film Collette plays Annie, an artist who makes macabre “real-world” doll’s houses, and who along with her family descends into a nightmare prompted by the death of her sinister mother. Also starring Gabriel Byrne, Ann Dowd, Alex Wolff, and Milly Shapiro, it premiered in January at midnight at the Sundance film festival to great acclaim, sparking instant Oscar-buzz for Collette, which seems long overdue. In what looks to be a huge year for her, she is also starring in the hotly tipped BBC/Netflix series Wanderlust this autumn, as a therapist who re-evaluates her life following a near-death experience.

Since grabbing international attention in only her second role, 1994’s enduringly charming Muriel’s Wedding, Collette has starred in a wide variety of films including 1999’s The Sixth Sense (another horror film that isn’t just a horror film), Little Miss Sunshine, About A Boy, Emma, Japanese Story, and Glassland, as well as television series including United States of Tara and Tsunami: The Aftermath. She has also appeared in Broadway musicals, including The Wild Party for which she was nominated for a Tony award. (Collette also sings with her band, Toni Collette & the Finish, featuring her husband Dave Galafassi on drums, though that’s stalled for the moment: “I’m too busy with my day job.”) However, despite garnering numerous prestigious awards and nominations, (including an Emmy and a Golden Globe for United States of Tara), there’s been no nod from the Academy since she was nominated for best supporting actress for The Sixth Sense.

Perhaps Hereditary will change all that. Collette is long-renowned for her expressiveness, with a particularly strong suit in “everywomen” who turn out to be anything but – it’s almost as though her molecules reassemble for every new role. In Hereditary she goes all out, emoting brittle, grief-stricken, broken, resolute, angry, frustrated, and everything in between. When I speak to Aster on the phone, he says that choosing Collette was “a no-brainer. She always struck me as a chameleon, disappearing into whatever role she was in.” Aster also liked the fact that Collette hadn’t done anything like Hereditary before: “Everyone knows that Toni is wonderful and amazing, but it’s seldom that we’ve seen her really tear apart the scenery in the way that this film demanded. She’s playing someone very tortured and conflicted, and really jumps off at the deep end. I told her that I was looking for a kamikaze performance, and she delivered.”

We meet at a central London hotel, where Collette, 45, is enduring what must be a packed, exhausting publicity schedule, and, despite her reservations about horror, seeing Hereditary again at London Sundance (good luck to her – towards the end it becomes too full-on and gory even for my tastes). When Collette gets up from her seat to greet me, it’s a lightning flash of huge blue eyes, wide distinctive smile, biscuit-tan and sandy blond hair. Her striking clothes, including a Victorian-style top and long sculptured skirt, lend her a wonderfully sub-gothic air, a bit like a sun-kissed Miss Havisham. (“No,” she says, later, “I was never a goth.”)

Engaged, friendly, open, with an unexpected splash of new age beach hippy in the mix, there’s just one point toward the end of our conversation when Collette becomes distracted and fidgety. I’m starting to wonder whether she dislikes the questions (or me), when she suddenly slaps her hands on her knees, and cries: “I REALLY have to pee! I’m so sorry, I had a bunch of waters. Would you please excuse me?” She dashes out of the room, returning a little later, restored to her chatty self. Elsewhere, a couple of times, a flicker of jet-lagged weariness pinches her features. When I ask if she’s looking forward to returning to her native Australia (to her home, in Sydney, with Galafassi and their two children, daughter Sage, 10, and son Arlo, 7), she mock-dramatically sags her shoulders, and hisses “Yes-sss!” with a ferocity that seems only partly in jest.

One intriguing thing about Hereditary is how dominant, disparate, and sometimes dislikable all the female characters are. If anyone takes on the soothing nurturing “caretaker” role, it’s Byrne. Collette’s Annie is far from the generic “good (bland) mom” figure so often seen in films. “I love that,” says Collette. “It just turns this kind of idyllic idealised myth of what it is to be a mother completely on its head. She’s so real and multilayered. It’s so rare to play a woman that feels as complicated as she does.”

Collette has played several on-screen mothers – what kind of mum is she in real life? “Well, I think there’s no one way of being, we are all many things. Also, life has changed, so those things keep changing too. So it’s hard to say without simplifying one of the most profound relationships one can have. And I try to bring that message to all the mothers that I play – yes, they’re mothers, but they’re whole complex creatures on their own.” And her children? “My kids are the most important people in my life, I’m entirely in love with them. But I don’t own them, they’re not reflective of me. I just try to guide them, to support them, be there, give them as much as I can, without being in any way dogmatic or didactic. And I learn from them, it’s entertaining. They’re very much their own people.” She smiles: “If you start to break anything down, it becomes more and more complicated, doesn’t it?”

Collette was raised with two brothers, in a suburb of Sydney, as part of a close-knit working-class family. “I can’t imagine my life without my parents,” she says. “They’re such a huge part of who I am, and they’ve overcome so much, and been so selfless.” Collette’s maternal grandmother died giving birth to another child, and Collette’s father was sent to Vietnam. “A lot of people still don’t know that Australians were involved in that war,” says Collette. “And he was drafted, he wasn’t in the army – he had the wrong birthday, and suddenly he’s got a gun on his back and heading off. It was terrifying, and he was just a teenager.” Did her father ever talk about it? “A little bit, as much as he felt able. It still affects…” She pauses: “With vets, it still lives with them, you know. It’s in there.” She presses her hands to her chest. “The body absorbs so much. It lives with you.”

One odd feature of Collette’s childhood was when she convinced everybody that she had appendicitis, which ended with her having an operation to remove the healthy organ. “Some people say, ‘Oh, that was your first role’, but it was nothing to do with acting. My mother had told me that her appendix was removed when she was 11, and I thought, ‘Well, I’m 11 now, I’ll give this a shot’, and it just kept going. Then it was too late.” It sounds almost like Munchausen syndrome, but Collette says that she didn’t fake the symptoms: “I felt pain in my stomach, and it just kind of escalated. Obviously, I didn’t understand what I was doing, I was 11.” Now she just finds the whole incident mortifying: “I’ve always thought that I’m not one of those cliched actors who got into it because they need attention. But perhaps there is an element of that? How embarrassing!”

Her parents allowed her to leave school at 16 and pursue acting, which sounds brave of them, and very determined of her. “They were really concerned when I decided to leave school and be an actress. Can you imagine hearing that from your teenage daughter? That’s a horror film in itself!” She’s described her youthful self as having “crazy” amounts of confidence. “I had this knowledge within me that this is it, this is what I need to do. I was just very strong-willed. I didn’t let any negativity or fear get in the way. I was so clear and positive about what I was trying to do. It didn’t mean that I didn’t feel nervous or inadequate. But a door would open, and I put a foot in, and suddenly the door was completely open, and it just kept happening.”

Was it blind confidence, in a way? “Yeah, but that’s fine, it got me going. If I was in the same position now, I know more about life and the world, and I wouldn’t make the same decisions, but at that point there was something so pure about my bravery.”

This single-mindedness led to Collette’s breakthrough in Muriel’s Wedding, and an international career. (She lived in London for a while, and says she still views it as her second home.) People still quote Muriel’s Wedding dialogue at her – in fact, I nearly do (“You’re terrible, Muriel”), but I restrain myself – it could be the 10th time she’s heard it today! But Collette says it never gets irritating. “I’m so fond of that experience and that character. It’s 25 years ago! When you go into a film, you connect to something and hope for the best. But to have that kind of reaction for what seems to be for ever is incredible.”

In her 20s, early success, on top of the usual stresses of being a young woman, threatened to overwhelm her, and Collette developed bulimia and suffered panic attacks. In retrospect, she thinks there was just a lot of change going on in her life, perhaps too much. “For most people, change can be very confronting.” She found the publicity side of her job particularly difficult: “I was unformed, a baby, working on instinct, and suddenly I had to form ideas and have opinions on everything, and not just conversationally and privately, these things were plastered everywhere. I had to grow up very quickly.”

I’d read somewhere that losing the weight she’d gained to play Muriel triggered her bulimia, but Collette thinks not: “I don’t think it was in a direct response to putting on weight for the film. Anything like that is more about control. My life did feel a little… fast. And I guess that was my way of pathetically trying to deal with it.” Well, that happens. “It does happen – it’s really common. And I’m sorry for the person that I was then. It just feels like another human being.”

She suffered panic attacks for several months. “But I haven’t had them since. You know how I was talking before about how the body absorbs everything? So, even if you can’t look at something, or address things in an open way, it does catch up with you. Your body will go: ‘Hello, I’m here, you do need to look at this!’ I think that’s what panic attacks are. I wouldn’t wish one on my worst enemy.” What does a panic attack feel like? “Erm, you basically feel like you’re dying. It’s not just being a little bit nervous, it’s deep, deep anxiety.” When I say it sounds as though it was a very dark period for her, she demurs: “Not all of it. I wouldn’t paint it that way. That was part of my life, but I was also having the time of my life. I was in my 20s, that’s what that decade is for, I guess.”

Collette also developed a penchant for shaving her head, but that seems to be more of a positive thing: “I’ve shaved my head five times in my life. I find it very cleansing.” Is it a style/fashion thing? “Not at all. It’s for me. It feels like a clean slate. I did it for a friend’s fashion show, I did it for a film, I did it for two films actually. But the first time I did it, I turned 25, I was in Mexico, I’d had probably too much tequila, and I walked past a barber, and I looked at this guy, I looked at his chubby fingers, and I thought: ‘I trust him, I’m going in!’ So, it was on my 25th birthday, I decided to shave my head.”

She grins: “The third or fourth time I shaved it, it was about three days after meeting my husband. I think it was, like: I’m just going to see how he reacts. It was like a test. Which is ridiculous.” It was a test he obviously passed? “Yes!” Was it your way of saying: this is me, unadorned? “Yeah, I suppose so.” When I ask if she has any tattoos, she confirms that she has several. Would you say that you’re impulsive, in a good way? You like to stir things up, just for yourself? She looks thoughtful: “Yeah, I think it’s good to do that.”

Certainly, there seems to be a key element of not so much impulse as instinct in how she chooses roles. She says that it’s always the writing that first attracts her, but aside from that, “it’s beyond something cerebral. If I start to think about it too much, and I’m on the fence, umm-ing and ahh-ing, then I know it’s not for me. Because it’s usually very immediate, a visceral gut knowledge that…” She makes her eyes pop fiercely. “I’ve got to do it.”

Didn’t you once say that if you couldn’t act, you would wither and die? “That was probably a very old thing that I said. I think, initially, I used acting as a way to express myself. I was very good at seeing other things very clearly, and I saw myself less clearly. And there were times when I felt overwhelmed by my own emotions. So acting became a way of accessing those emotions and doing something positive and creative with them.” A form of catharsis? “It is catharsis. But that was when I was much younger. My relationship with acting has changed, and deepened, and continued to change. That’s inevitable.”

Collette was speaking out about issues such as body image and female representation in Hollywood long before the recent explosion with Harvey Weinstein and MeToo/Time’s Up. She tells me she’s always enjoyed working with female directors (“I just wanted to work with great directors of either sex”). Has she ever experienced harassment in the industry? “No.” Would she define herself as a feminist? “I would say that I’m both a feminist and a humanist. I believe in equality, I always have. So, the idea that this behaviour has been occurring…” She sighs. “It’s not a new thing. But it’s just so incredible, and it’s so necessary, and actually exciting, that people are speaking out about it now. It takes a conversation for there to be action and change.”

Collette feels that it’s bigger than her industry, it’s society at large. “There’s a huge imbalance – and there has been for longer than my lifetime.” She also thinks that there’s been a genuine change of attitude in Hollywood. “You need awareness to be able to make a change, and you can’t help but be aware of it now.” What about unrealistic beauty/body image ideals – this idea that, with women, it’s first and foremost about the visuals? “Well, that’s bullshit! I’ve never believed that. And I think, if that’s been the notion, which I know it has, it’s an archaic notion now.”

It’s at this point that Collette decides that she needs to wee, bustling out of the room in her voluminous skirt. When she returns, we discuss President Trump. “Who knew this was going to happen? I mean, wow, it’s just a really incredible moment in time, isn’t it? You can hardly believe it. How is this person getting to that position? It’s hugely frightening – it’s an absolute doozy!” We also talk about antipodean female politicians, including how New Zealand prime minister Jacinda Ardern’s pregnancy seemed to draw criticism that she wouldn’t be able to do a proper job. “What kind of idea is that? It’s so archaic. It has nothing to do with someone’s ability at work. I don’t think that [attitude] exists in one part of the planet, it’s everywhere,” says Collette. “It’s a sexist, ageist world… It is changing. Just not fast enough.”

As the interview winds up, we discuss her future projects, including Wanderlust written by British playwright Nick Payne, which will air on BBC One this autumn, in which she plays a woman whose brush with death makes her question her life, including her commitment to monogamy. “But it’s beyond that – it’s about what’s informing her decisions. So, even though I’m playing a therapist who’s very astute and aware, she has her own awakening of sorts. It’s a perfectly woven psychological web,” says Collette with relish.

These days, she would work in Australia all the time, if she could, just for family reasons. She’s often described herself as “nomadic”. Is that grating a bit now? “It’s not grating. We’re all adaptable. My family has moved around so much, but we know that home is Sydney. It’s just a feeling, you can’t help it, there’s only one home. And my parents aren’t getting any younger. My tribe is there, and there’s a kind of calling to return.”

Collette has her own production company, writes, adapts material, and has her eye on directing. “I want to be involved earlier in the creative process,” she says. “As an artist, and even as a human, you need to challenge yourself and grow. You never stop learning. It keeps me curious, open, awake and alive. All of those exciting good things.” But acting still challenges her? “Of course!” she says, widening her eyes. “It’s still self-expression, you still have to make it feel honest for the audience to believe it. It’s a matter of empathy and understanding. I think, if anything, that’s what drives me – trying to understand what life is. It’s all a mystery.”

Hereditary is in UK cinemas from Friday, and out now in the US and Australia