For 35 years the former nurse had hoarded clothes, furniture and knick-knacks at her Eastwood home. She collected junk from the roadside and haunted garage sales and op shops, "stuffing the house with objects".

The accident made her realise her daughters would be burdened with disposing of her possessions if she died.

"For 12 years now, I've been decluttering," she said.

Ms Nicholas felt she had lost control over life. She suffered from post-natal depression and obsessive-compulsive disorder, and cared full-time for her mentally ill husband and daughters. But hoarding restored a sense of control.

"There's also a real vacuum if you don't have enough love and connection in your relationship," she said. "Your identity becomes bound up in stuff to give you self-esteem."

The 72-year-old is proud of tackling her problem but "overwhelmed by what I still have to do. I don't want to be caught short and die before I've finished this exercise."

Hoarding is a growing problem in Australia. The fourth National Hoarding and Squalor Conference, to be hosted in Sydney from June 29-30 by Catholic Community Services NSW/ACT, aims to raise awareness about the impacts.

Keynote speaker Randy Frost – professor of psychology at Smith College in the US and author of the bestselling book Stuff – said between 2 and 5 per cent of people suffer from significant hoarding.

Some cannot throw things away because of a strong emotional attachment, he said, while others are "concerned about waste and about losing an opportunity".

Professor Frost said hoarding disorders are "simply an exaggeration of what we all do. For all of us, possessions have an essence that goes beyond their physical characteristics. For people who struggle with hoarding, their sense of meaning for an object is more exaggerated."

Those with hoarding disorders have an "aesthetic sensitivity", he said, making connections with things and paying attention to things that most people don't.

"You can think of it as a form of giftedness, an appreciation for the physical world that the rest of us have lost, or maybe never had," he said. "But at the same time it's a curse, because there's so much stuff coming into their possession that it crowds everything else out. They're collecting life without living it."

Catholic Community Services' manager of hoarding and squalor, Mercy Splitt, will also speak at the conference. She said Australia lacked a national strategy to address the problem, which is estimated to affect 600,000 people – up from about 400,000 in 2012 – at a cost of $1.8 billion.

Hoarding was included in the American Diagnostic and Statistical Manual of Mental Disorders, the "psychiatrists' bible", in 2013. But it is more than a mental health issue, drawing on the resources of aged care and community services, local councils and governments.