I had yet to release an album when I was invited to play the Bendigo leg of Groovin the Moo festival in May 2017. Up until that point the biggest shows I had played had been to about 400 people in Melbourne.

Montaigne was on the festival lineup and she was unwell so they shuffled everyone around. Amy Shark – who was riding the wave of Adore and having a real moment – got bumped from the big tent to the main stage and they upgraded me and my band from the fucken car park or something to the big tent.

It all happened quickly, so the likelihood that the information was disseminated to the entire crowd was very unlikely. We got to the gig and just before we came on I saw the tent had like 7,000 people in it. I thought: “Fuck. All these people are here to see Amy Shark and she’s not going to come on stage. It’s going to be me!”

I walked on and the first thing I said was: “I’m really sorry, I’m not Amy Shark, but my name’s Alex Lahey and we’re going to play a really good show for you.” There were a few boos.

Up until then, I had always played small rooms and I felt really comfortable in that domain, so it wasn’t until my mouth opened and we started performing the first song that I was like: “Holy shit, I have enormous stage fright.” I Love You Like a Brother was the opener and there’s not much room to breathe in that song. I was trying to suck in as much air as I could and keep my balance. My knees went really weak – they turned to jelly. I had that sensation where you’re simultaneously really cold and sweating.

There were these big LED screens behind the stage but we hadn’t prepared anything for them, so they put up stock images of flames the entire time – it looked like some kind of Tool show with this white girl singing indie rock.

I felt really dizzy and funky. It was so out of any reality I had considered – staring down the barrel of 7,000 people in front of me with flames on this screen behind me. It was like a runaway train.

Once my legs stopped shaking I was trying to do my best Bruce Springsteen. He’s the ultimate arena big-crowd rock’n’roll dude. Whenever I think: “How do you capture that audience in those massive situations?” he’s the guy.

I was thinking: “This is a beautiful accident and it might never happen again, so just have a great time – be in the moment and enjoy it.”

The second-last song we played was You Don’t Think You Like People Like Me. It had made the Triple J Hottest 100 that year and when I saw people singing along, that’s when the “I have to win you over” mentality left and I could just enjoy the show.

When the adrenaline kicks in, you let it take you away and you respond to that. I had this half-hour window where I had these people who hadn’t come to see me, but – and this was the thing that baffled me – they all stayed.

I was playing a white Fender Mustang and at the end of the gig I threw my guitar to my stage tech – it was one of those rock’n’roll things I had always wanted to do. There’s a great photo where the guitar is in mid-air and going to him. It was a classic Bruce move. When we got invited back to do the entire Groovin the Moo festival tour the following year I did the same guitar trick but I didn’t throw it far enough and it just slammed straight to the ground. That guitar has now done its dash.

That 2017 Groovin the Moo show was me simultaneously living out a fantasy and trying to figure out how to do it. It was the breakthrough moment – a real zero-to-hero experience.

• Alex Lahey’s latest single Spike the Punch is out now. See here for her upcoming tour dates