The illness that almost killed Gretta Ray announced itself slowly. First there were chills that had her inexplicably shivering under the doona. Then came gastrointestinal symptoms; next a splitting headache. Fatigue flattened her, keeping her in bed for days. But it was when the singer-songwriter woke up one morning with double vision that she knew something was really wrong. Ray went straight to hospital – and stayed there for six weeks. After a long and agonising slew of tests, she was diagnosed with infective endocarditis, a life-threatening infection of the heart that can cause a strange, gradual march of symptoms.

Ray was put on an antibiotic drip "pretty much 24 hours a day", which saved her life. But at just 26 years old, her age made her an outlier on the cardiology ward – and forced some big psychological reckonings.

"Being young and being motivated and ambitious, you think you're invincible, and you're not," she says. "The scariest part of it all was not being able to be told that I was going to be OK … That's going to live with me for ever, and there are still times when I find myself getting anxious and thinking those terrifying thoughts – like, 'maybe you'll die'."

If her words leave a heaviness hanging in the air, Ray doesn't leave long before puncturing it. "Welcome to my trauma-dumping session!" she laughs.

Ray is now two years on from her hospitalisation, but has the natural pep that belies someone who has been through such an ordeal. She is warm and enthusiastic, eloquent about what she has been through with her health, if pausing occasionally to wave away the emotion that swells when recalling particularly difficult moments. We are crammed in an intimately small meeting room at the office of her record label to talk about her new album, Heartsong, one that documents not that terrifying encounter with illness but the "aftermath of that situation – how my life imploded after the fact".

Before she was struck by that cascade of confusing symptoms, Ray had built the foundations of a promising music career. She got her big break at age 18 when she won a Triple J song competition. That led to a major-label deal with EMI and two albums of bright, sunny pop music, the latter of which, Positive Spin, saw her play 50 tour dates in 2023, including her biggest headline show to date, a gig in London to a crowd of 600. She hadn't quite had her star-making moment yet, but to Ray it felt as if she was on the precipice of something very exciting – and was very hungry, as she describes it, for a kind of success that looked like "playing the biggest rooms". Her mentality was that she had to be "everywhere all the time", doing every single promotional task she could in service of pushing her career forward. "Full teacher's pet of the industry was what I was giving," she scoffs.

So in mid-2024, Ray packed up and moved from Melbourne to London together with her then-boyfriend, where she planned to embark on the next chapter of her career.

"I was going to write another record. It was going to be even more pop. I was going to be bigger; shinier!" she says, gesturing expansively with her hands. "And then two days into being in the UK, I went to the emergency room."

So began the implosion. Ray stayed in the UK for another month after her discharge from hospital until she was fit enough to fly home to Australia, "heartbroken" to give up on her London dream and return to where family could support her. Then a week after returning home, Ray's best friend's mother died; three days after that Ray and her boyfriend broke up. "I was so riddled with anxiety. I was having panic attacks left, right and centre. I was seeing multiple therapists trying to get a handle on how traumatised I was," she says. Physically, Ray contended with major weight loss and weakness, as her weeks spent bedridden had wasted her muscle mass.

And she was forced to step back from music, cancelling her remaining tour dates for the year and having to retrain her vocals from "level zero" after illness drastically altered her lung capacity. Ray found herself overwhelmed by grief for the career that suddenly seemed out of reach, and confronted with the crater-sized hole it left behind.

"I was trying work out my life was going to look like," Ray says, slowly enunciating each word. "My whole identity had been wrapped around this project for my entire adult life … I had to stop my job completely for the first time since I was 18, and I had no idea who I was outside of it."

After six months of things being "really bad" – time she spent slowly rebuilding her strength and darting between endless specialist appointments, while sitting with the loss of her career and relationship – Ray eventually turned a mental corner, where "every single day of January was perfect, because I'm alive! I think a lot of people who have gone through big significant sickness things experience that. I was so grateful to have made it through."

Feeling happy, and desperate to stay that way, she took herself to the studio to try to write "my upbeat pop stuff again, about having the summer of my life". It didn't work.

"I would hate the song. I would get really bad writer's block," she says. Instead of returning to her earlier sound, Ray felt a creative force pushing her to look back and excavate all she'd been through. "And then I would start writing about something real and honest and painful, and the song would come."

It proved healing – and fruitful. Six months later, armed with 50 demos about sickness, breakups, grief and recovery, Ray began a four-week recording session at Matt Corby's Rainbow Valley Studios. Corby and Ray's longtime producer Gab Strum became her key collaborators on an album that sounds very different to her previous work; soft, lovely and unpretentiously poetic folk music à la Lizzy McAlpine or Julia Jacklin rather than major label pop. Ray loved "that it sounds nothing like the last record" and called it Heartsong, a title with a very significant dual meaning.

Heartsong is an ode to all Ray lost and rebuilt after her illness. She sings about the relationship that couldn't survive the pressure of her ill health, and the agony she felt when well-meaning friends would play her old songs over the car stereo, back when all she could "think about was just how desperately I wanted to do that thing, be in my life before". But there are also the tracks about the first gasps of happiness – the moments of "wait, I'm laughing again; I haven't laughed in ages!" – that eventually started to appear. On the delicate, airy lead single Swimming, Crying, Ray nods to the healing properties of Sydney's saltwater. She had visited the harbour city a few times during her recovery and became "addicted" to ocean swimming – so much that she decided to move there, trading the home town that felt haunted by the worst days of her life for a fresh start by the water.

That's not the only change Ray made in her life after a core-shaking two years. Ray feels she now leads "a better life" than she did before – one with less stress and more meaning. Moved by how much her friends and family showed up during her recovery, she now prioritises those relationships above all else, no longer that person with dozens of unanswered texts in her phone. She is "so protective" of her health, bearing a responsibility to maintain great cardiovascular fitness for the sake of her heart. Because while she has made a full recovery, infective endocarditis left Ray with a damaged mitral valve that must be monitored with regular echocardiograms. Having never been able to trace the initial illness, Ray has had to make peace with the fact that she will likely never know what caused the infection – and lives with the knowledge that she is more susceptible than the average person to getting endocarditis again.

Ray's relationship with her career has changed, too. She feels she has a renewed purpose to share her music, but has let go of the internal pressure to "build this empire of Gretta Ray" that once defined her.

"When Positive Spin didn't get nominated for an Aria, I was so devastated. Which now I think about and I'm like, girl, there are worse things. But it was all that mattered to me," she says. "And I just can't have that become my life again."

Her aspiration for Heartsong is for the songs to help people through their grief, the way they helped her when she was writing them. The album ends on a swelling, sunny track called Lucky (In My Life) on which Ray sings the line: "Get sick, get well, get by/How lucky am I?" Because on balance, after all that's happened, she feels she has plenty to be grateful for.

"I need to acknowledge that that time was terrible. It was awful; horrible for my family … And I hate that they had to go through that. That's real and true," Ray says. "But the way in which I was taken care of, the way in which I recovered, the friendships that I have, the music that I was able to make and the life I get to lead now – all of those things – that's extraordinary luck to me."

• Heartsong is out on 30 October.

Gretta Ray's songs to live by

Each month we ask our headline act to share the songs that have accompanied them through love, life, lust and death.

What's a song you wish you wrote?

Conversation by Joni Mitchell, because of how much I love the lyric "she removes him like a ring to wash her hands, she only brings him out to show her friends". I feel like I've spoken to dozens of songwriters about how much I adore that line.

What's one song you wish you didn't write?

There are certain lyrics in my older songs that are very gushy that I cringe to listen to now. On my second EP there's the line "I wait at home to greet you, I'll treat you like you're a God", but I would never wish I didn't write it! I think songwriting documents exactly how you are at a particular point in time, and ultimately showcases your growth. I would never write that lyric now, but I totally understand why I felt compelled to write it at 19.

What is the last song you sang in the shower?

Massachusetts by Jensen McRae. We're on tour right now across the US, and all of her incredible songs are in my head constantly.

What is the song you have listened to the most times this year?

I have albums on loop rather than singles. The first half of this year it would be Audrey Hobert's album Who's the Clown?, and I can guarantee that the second half of this year it will be Lizzy McAlpine's album Angel. I'm listening to it so much.

If your life was a movie, what would the opening credits song be?

Right now, it would be The Heart is a Muscle by Gang of Youths.

What is a song you loved as a teenager?

I loved (and still love and worship) Steer by Missy Higgins.

What is the first song/album you bought?

The first album that was mine (gifted to me on my seventh birthday) was Kylie Minogue's Ultimate Kylie CD. It is just as important to me now as it was then!