It's a fear that lurks at the bottom of many middle-aged, middle-class psyches.
The house, the job, the relationship - it can all change overnight because of circumstances beyond your control.
Your marriage goes west and the joint property goes with it. You get made redundant and the mortgage repayments can't be met. ACC won't cover that injury that puts you out of work for six months.
But before you end up on the street, there is a second-to-last resort - flatmates.
It's hard to tell how many people over 40 are cohabiting in a non-conjugal sense, but the percentage of older renters, as opposed to owners, has been increasing steadily for several years.
They constituted 10.7 per cent of renters in 2001 (58,572 people), 10.6 per cent in 2006 (64,701 people) and 12.7 per cent in 2013 (98,529 people).
Pru* is in her 40s, moved to New Zealand from Europe 14 years ago and shares a lovely Ponsonby house with flatmates in their late 30s and early 50s. She'd prefer not to.
She doesn't hesitate when asked what the pros and cons of senior flatting are.
"There are pros?" she enquires. "It would be me and the dog, if I had my way."
For her there is only one good thing about her situation. The money she saves.
"I would have moved out of the city if there was dependable public transport," says Pru, who works in town. "But there isn't, so I'd have a two-hour commute if I lived anywhere I could afford. That's why I don't own a place in Pokeno. The only affordable alternative in Auckland is to rent and to share. It would cost twice as much not to have flatmates."
So she makes the best of what she sees as a bad deal. The house's occupants are a lawyer, a CEO and an accountant.
And Pru says her flatmates are of the same view when it comes to how much they enjoy sharing a fridge at their ages.
"We avoid each other as much as possible. Our living arrangements are very separate. If we want to hang out we can, and we're quite happy to be social when we want to be but we have no obligation to each other socially."
Pru says one reason she's open to taking shelter with others is that she doesn't come from a culture where home ownership is prioritised as much as it is for New Zealanders.
To her, the great Kiwi home-owning dream looks like a nightmare - or at best a very unsettling hallucination. "After all these years here, I still think it's peculiar," says Pru.
"I have Kiwi friends who can't have a life because their mortgages are so high. So they sit at home all the time, in the house they're struggling to pay for."
Dave Watson, who has just turned 50, is also sharing for financial reasons, although he is used to owning his own home.
"I've owned a house for the last 20 years and have had a marriage breakup, so I have left the family in the house and I am flatting. And I've had to find a place close to where the kids go to school so we can work in together."
That meant finding a place in Mt Eden, which "is really hard and expensive".
"There's a bunch of shit out there that people rent out and don't do any work on. So I've ended up with a three-bedroom house and had to get a flatmate to make financial sense of it."
Watson, who flatted in his 20s, says it feels like going back to the beginning and starting again.
"I've had to get used to the whole idea even of just sharing a space."
And his domestic situation created special difficulties. "I only wanted one person, and I wanted a female because I have a 15-year-old daughter so need to be wary around that."
Watson has had two flatmates. "When I got the lease it took me about four weeks to find somebody. Then I probably had three weeks to find the next person. To get a good match is quite problematic. Not having rent in those four- and three-week spans adds up to quite a bit of money."
He's laissez faire about the mixing and mingling side of things.
"I just let that be. If they want to engage, that's cool. If they don't, the room is big enough for someone to disappear into if they want to.
"I'd want someone who was working - not just hanging around. And I wouldn't have someone who couldn't communicate when they needed to and do it clearly and honestly."
Does he think he could get to like it more than he does? "If it was the right person I could enjoy just having someone as a flatmate. My work is in sustainability so sharing resources makes sense to me; it would just have to be the right set-up."
He is even open to the idea of buying a house with a flatmate, which was, in fact, how he bought his first home.
Surely it's not all room and gloom? Well, it sounds like it might be, certainly if comments posted to a blog about the difficulty older people have being taken on as flatmates are anything to go by.
Your marriage goes west and the joint property goes with it. You get made redundant and the mortgage repayments can't be met.
"The overall pattern (only from my own experience)," says one, rather negative commenter, "is that older flatmates tend to have unsolvable problems, such as alcoholism, violence issues, the inability to hunker down to paying rent, mental illness for which they WON'T seek treatment, or other related problems."
And that would be their good points.
Asks another, presumably rhetorically: "Do you really want to be in middle age and worrying about someone taking your food, or breaking something, or not paying their bills, or trying to convince the landlord to fix something or not having enough space to do what you want? I couldn't stand it."
Grey Power national president Tom O'Connor thinks shared accommodation has more going for it than Pru does, especially for the people his organisation helps.
Once mortgages are a thing of the past, money is not so much of an issue.
"When younger people go flatting together it is usually a temporary arrangement," says O'Connor. "For older people such arrangements are more likely to be long-term and issues of compatibility become more important.
"It is certainly a better option than living alone but older people are usually less adaptable and more set in their ways."
Sadly, the oft-touted option of grandparents moving in with their offspring and grandchildren to be a wise and helpful old presence around the family is also under financial pressure.
"Young people with growing families are generally less able financially to include grandparents in the home than they were a generation ago," says O'Connor.
Many older people are likely to have reduced incomes and that can see them open to the idea of flatmates. However, Age Concern's chief executive, Stephanie Clare, points out that soaring accommodation costs and a housing shortage are national issues that don't just affect older people.
She notes there are plenty of non-financial advantages to living with other people in later years.
"There are a lot of benefits with the likes of social isolation," says Clare.
"There are wellness benefits, both nutritionally and physically. Behaviours like eating together and doing stuff together just increase your overall wellbeing."
Clare observes this may require a shift in older attitudes.
A person who has no money worries but is on their own might not see the advantage of having a flatmate for other benefits, such as social wellbeing.
I've ended up with a three-bedroom house and had to get a flatmate to make financial sense of it.
The baby boomers, as is their wont, are skewing the data in new directions, the long-term results of which are still impossible to discern. But there's no disputing that whereas previous generations lived with their parents until they got married, now there is a cohort of 65-plus people who went flatting in their 20s and may be more receptive to the notion when they find themselves widowed or separated.
Sam Coutts, director of Chase Property Management, is a letting agent who knows more tenants than most people do and thinks older flatties might be a lot easier to live with than certain blog commenters would have you believe.
"As you mature as a person," says Coutts, "you should be a bit more well-adjusted and keep on top of things like the housework, perhaps more than young people do."
He agrees the benefits to sharing are both financial and social.
As for the former, it's simple arithmetic: "If you spend a little bit more you get a nicer, bigger house. And if you combine your resources you've got a lot more money a week going for a nicer property."
The hidden, non-monetary cost of the financial benefit is eternal vigilance - renter beware is Coutts' advice.
"It always depends on the people. You have to be cautious. You need to know who you're living with because your home is your sacred space.
"You need to know how often they'll be home, if you're living with great people. You can be trapped in a home where you feel awkward."
Which won't happen to Pru, although she's realistic about the likelihood of her situation changing, which she says it certainly will "when I win the lottery".