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Worrying appropriately about real concerns helps keep us safe, but too much fear can ruin people's lives. Kim Dungey investigates.
When Katy's anxiety disorder was at its worst, walking to her letterbox was a challenge and entering a supermarket, terrifying.
For three years she couldn't socialise, hold down a job or even drive across town to visit her mother.
''I found it hard to do anything outside the house. It was very debilitating.''
Twelve years on, she thinks there is still an anxious voice inside of her but won't listen to it for fear of her illness returning.
''I just won't play the game anymore,'' she says.
''It's a horrible place to be.''
Katy is not alone. Anxiety disorders are now the most commonly diagnosed mental illness in the world - less publicised but more prevalent than depression - and the subject of thousands of studies highlighting the complex genetic and environmental factors at play.
As a teenager, Katy worried much more than other young people about going to parties.
In her early 20s, she had her first panic attack while driving to work.
The blurred vision, racing heart and rapid breathing were so frightening that she immediately returned home and this quickly became her coping strategy: ''By doing that, I gave the anxiety the power and it wasn't too long after that that I developed agoraphobia''.
''Anxiety is a survival instinct. It keeps us safe,'' says the 44-year-old, who moved from Christchurch to Dunedin four years ago.
''It was just that my sense of danger was more heightened so I could see danger where there was none.''
''Supermarkets and shopping malls were really bad because there were lots of people and it was a long way to get out to safety. I had to have an escape plan.''
Neither anti-depressants nor self-medicating with alcohol helped and when she saw an advertisement for an agoraphobia support group, she was ''absolutely bewildered how anyone would turn up''.
She also hid her anxiety from others, knowing they wouldn't understand: ''I didn't understand. In that way, it's very isolating.''
Emma Barker, of the Anxiety New Zealand Trust, says anxiety disorders affect 20-25% of New Zealanders at some point in their lives, are twice as common as depression and a leading cause of absenteeism from schools and workplaces.
While the biggest age group seen at the Auckland clinic is late teens to late 30s, the trust has treated children as young as 5.
''Everybody will experience some anxiety at some point in their lives but where it takes over one's life, is interfering with everyday activities and causing significant and persisting distress, then we call it a disorder.''
The term includes panic disorder, post-traumatic stress, specific phobias (about things such as snakes, storms, heights or needles), social anxiety (a fear of situations that might lead to negative scrutiny by others), generalised anxiety (where people constantly worry about everything) and obsessive compulsive disorder (characterised by intrusive thoughts and repetitive behaviours).
Dr Christopher Gale, a senior lecturer in the Dunedin School of Medicine's department of psychological medicine, has known people who have taken two hours to get inside their house, five hours to sort their recycling and 50 minutes to wash their hands before dinner.
Others have recurrent, distressing thoughts about the things that society finds most repugnant, he says.
In less secular times, these often centred on offences against religion; now it is more common for them to think they are going to abuse their children.
Research shows that as well as often being accompanied by depression, anxiety disorders tend to show up young and to be connected.
One study, by Harvard psychologist Jerome Kagan, found that 10-20% of infants are more timid than their peers and that they continue to have higher heart rates, faster startle reflexes and more stress hormones throughout their lives.
Yet research has also found that while certain genotypes make you particularly vulnerable to psychological breakdown when subjected to stress or trauma, other genotypes make you naturally resilient.
Barker says some people are genetically disposed to develop anxiety but whether it develops into a disorder can depend on what life throws at them and whether they enjoy protective factors such as living in a stable environment with lots of social support and whether they have adequate sleep, regular exercise and good nutrition.
Though she doesn't want to blame parents for creating anxious children, there is also ''an element'' of people learning to agonise about certain things if they are around others who worry.
Why, though, would rates of anxiety be increasing when life expectancy and standards of living in the Western world have never been higher?
Barker says the the fight-or-flight response that helped cavemen escape sabre-tooth tigers is still wired into us, though these days the ''threats'' are things such as conflict, changing circumstances and performance issues.
''Life seems to be a lot more demanding, particularly for our younger ones these days. They've got higher targets to meet at school and there's possibly more focus on academic rather than social and emotional skills in schools ...''
Cherie, a Dunedin mother who has been diagnosed with an anxiety disorder and depression, believes part of the problem is the fast-paced world we live in: ''Everything has to be done to a deadline and those deadlines are getting smaller and smaller. It's not a caring society. It's `all about me'. And there are high expectations of what you should do and be, especially when you're a mum.''
Donna, who also has an anxiety disorder, says social media is a constant source of worry for teens, who are judged for how many friends and ''likes'' they have on Facebook.
Some blame the sometimes overwhelming number of choices that need to be made on a daily basis and the regret that comes from choosing poorly.
Others point to a loss of social structure, Dr Gale noting that anxiety disorders are more common in English-speaking countries where there is generally more freedom over everything from career paths to the roles that men and women assume.
Scott Stossel, editor of The Atlantic magazine, revealed his 35-year battle with anxiety disorders in last year's best-selling book, My Age of Anxiety: fear, hope, dread and the search for peace of mind.
A ''high-octane worrier'' whose wedding was accompanied by sweating so torrential that it soaked through his clothes and by shakes so severe that he had to lean on his bride at the altar, he writes that some people have always felt pathologically unhappy but that anxiety did not even exist as a clinical category half a century ago.
• By the 1960s, the Rolling Stones were singing of ''Mother's Little Helper'', the tranquilliser, diazepam (also known as Valium), which was popular among housewives.
Today, selective serotonin reuptake inhibitors (SSRIs) have so saturated the American culture that trace elements of the antidepressants have been found in fish in the country's largest reservoir, which supplies drinking water to Las Vegas, Los Angeles, San Diego and Phoenix, he says.
Stossel cites studies that question whether SSRI antidepressants are any more effective than placebos and that suggest long-time users of benzodiazepines risk cognitive impairment and dependence.
Despite this, he has spent the past 20 years on tranquillisers and antidepressants, believing they work at least a little, at least some of the time.
Many with anxiety disorders undergo cognitive behavioural therapy (CBT) - a type of psychotherapy which aims to change unhelpful thinking and behaviour - and exposure therapy - which is based on the idea that extended exposure to the object of fear, under the guidance of a therapist, will gradually make it less frightening.
''A bit of fear is useful ...''
Dr Gale explains.
''Fear is how we modulate risk. It's a signal. So it's better to learn to manage it [rather than try to expunge it] and that's why the talking therapies are the treatment of choice and the medications are to aid.''
Delivering those ''talking therapies'' to large numbers of people on time and on a budget, is a challenge, though, so he favours making more use of internet-based CBT programmes and coaching by practice nurses for those with a single anxiety disorder.
Psychologists could then be reserved for complex cases that need more time and more funding.
Cherie has used benzodiazepines in the past but dislikes the side effects and sees medication as a last resort.
Instead she turns to reading, music or exercise when she feels anxiety building and tries to focus on her son and keeping busy.
The 41-year-old, who regularly has panic attacks, was recently distressed to see her 7-year-old son having one, too.
''I'm teaching him that it's OK and he will come out the other side ...'' she says.
''People have told me to get a grip, snap out of it, stop being a drama queen, and it doesn't help. It's real for the people going through it.''
While she fails to see any upside to anxiety, some have linked it to intelligence and believe it makes people better workers.
Emma Barker says someone with generalised anxiety disorder, who tends to catastrophise events before they have even happened, will keep their family safe and be the sort of person she would want to employ ''because they'll be on time, they'll have everything covered and they'll be very organised''.
''But of course the negative flip side is that that person will also be worn down and exhausted by it. People with generalised anxiety disorders think a lot.''
For Katy, it was a significant birthday that ultimately proved a turning point.
''Eventually I'd just had enough of living like that ...'' she says.
''I remember thinking, `It's all right to be mucking around in my 20s but now I'm 30, it's time to grow up'.''
Soon after, she began 10 months of cognitive behavioural therapy at an anxiety disorders unit in Christchurch and confronting her fears one small step at a time.
Initially the goal was to drive from her home to the nearest lamp post.
The next time she went one lamp post further.
Learning what was happening in her body during panic attacks made them less frightening.
The day she managed to drive to her mother's house was cause for celebration.
Today the woman who was virtually a prisoner in her own home does not think twice before driving to Christchurch to visit family or boarding a plane to go on holiday.
''All the things that seemed impossible are now possible,'' she says, smiling.
For more information
• Do you need to talk to someone about anxiety, panic attacks or phobias? The Otago Mental Health Support Trust provides peer support for people with any experience of mental illness, including anxiety, and can be contacted during business hours on 477-2598 or 0800-364-462.
24-hour support lines:
• Anxiety New Zealand, 0800 ANXIETY (0800-269-4389)
• LifeLine, 0800-543-354
• Youthline, 0800-376-633
• Suicide prevention line, 0508 TAUTOKO (0508-828-865)