'That's really funny, if you think about it," Ruby Wax says, grappling to catch her breath through wheezing laughter, her gravelly voice ascending a couple of semi-tones.
"I never thought for one second that my own sickness would be a means to showbusiness," she says, engulfed in giggles.
"I mean, c'mon, who knew? I certainly didn't."
It's more of a career rebirth, really. Wax (60) has recently become the poster woman for mental illness, a mantle she wears proudly. Seven years ago, she experienced, as she calls it, "the tsunami of all depressions", and woke to find herself institutionalised in the Priory, unable to leave her chair for five months and staring catatonically into space.
The brash American TV personality had always suffered from depression, with bouts alternating every five years. It would generally last a couple of days, but steadily became worse as she got older.
"When I was young, we thought this was some kind of virus," she explains. "Nobody dealt with it. They just assumed I would get over it. Nobody knew anything at the time. I can't even remember the first time it happened. I probably just thought it was the flu.
"In college, I would go to bed for a few days and sleep, although it was more an awake sleep. The bouts started to get longer and the last time, the worst time, it was months – months of this semi-conscious state."
Inspired by her experience, she penned a one-woman show, 'Live From The Priory', with friend Judith Owens and played it to private and public mental-health institutions around the UK.
"It felt like we were giving the illness a platform, and those suffering from it – in silence for so long – a voice to talk about it. It gave me a voice to talk about it.
"There's nothing that a person with depression likes more than another person with depression," she laughs. "It's like sucking your thumb."
Many celebrities over the years have quietly alluded to their struggle with mental illness, from George Michael and Kylie Minogue to Jack Dee and Carrie Fisher.
Ex-boxer Frank Bruno and former comedy queen Caroline Aherne famously endured severe bouts and quietly slipped out of the spotlight soon afterwards.
Sufferers saw their illness swept under the rug by a media unable to define it, yet other physical illnesses, such as cancer and HIV, never left the headlines.
Two years after the placement in the Priory, Wax inadvertently became the face of mental illness after allowing her face to be plastered all over the London Underground for Comic Relief with a simple caption: 'I suffer from depression.'
"I thought it was going to be a small picture, on the backs of magazine, but no, it was a huge poster telling the world that I have depression," she says.
"I hurled myself in front of one and then saw another and hurled against that and then another going down the escalator. I just had to give up and come out of the closet. That's when I became the poster girl for mental illness."
Wax is a showbiz enigma: a woman who has crossed the line between stand-up and red carpet; stage and celluloid and has moved back and forth between fiction and reality TV.
With her wild hair, bold red lips and unmistakable drawl, she played to the American stereotype and became a regular fixture on our screens.
She was at the height of her popularity in the mid-1990s with her BBC series 'Ruby Wax Meets...' She leapt into bed with Madonna to discuss preferred sexual positions and later squeezed into a red swimsuit to run alongside the surf with Pamela Anderson.
She was the best, the bravest and the funniest interviewer in the business, armed with a razor-sharp wit that took little pity on fools.
I interviewed Ruby two years ago and had a traumatic experience. Each question was shredded on the spot and every awkward pause was greeted with a terse, 'Am I boring you?'
Speaking to her this time from her home in west London is an altogether more relaxed affair.
Wax has recently written 'Sane New World', an eye-opening account of her struggles with mental illness. She lists the methods and theories gleaned from her studies in mindfulness-based cognitive therapy at Oxford.
In it, she determines to discover "just what exactly is wrong with us", offering sections for the 'normal-mad' and the 'mad-mad'; the inner chemical workings of the brain; the use of mindfulness and how it can tame your mind – her champion cause – and alternative suggestions for peace of mind.
"When I do my show ['Losing It', honed and expanded from 'Live from the Priory'], it speaks to the one in four of us who suffer from mental illness and everyone in the audience is nodding their heads. There's a commonality that's wrong with us biologically; it didn't work out.
"I also wanted to write for the normal mad. It's all of us, the ones who struggle with their own voices.
"We're all living in our own private hell, sometimes in so much of a rush that we fail to see what's going on. We all have the same machinery up there and it's about being able to cope should the critical voices get too loud."
She also extols the virtues of mindfulness. Based on the concept of Buddhist meditation, it's been employed by psycho- therapists to treat stress, anxiety, depressive, relapse and addiction.
"I was very sceptical about learning something connected to meditation," she tells me. "I thought you have to use words like 'shurananamurtisugamutisatimanyannanaan', an explosion of meaningless letters or worship some elephant with a thousand arms.
"But it's not about emptying your mind, because even in a coma, it's still chattering away. It's like mental sit-ups which alleviate the emphasis on the 'gottas' – 'gotta do this, gotta write that email, gotta garden, gotta learn judo'."
"With mindfulness practice," she adds, "you eventually calm that bucking bronco of a mind, gently taking the reins and steering it where you want."
Is this something Wax has employed in her everyday life?
"Of course," she snaps. "Especially before I go on stage. I'll take time out to focus, so I don't walk out there and go blank and get red mist in my head."
Does she still believe in medicating?
"I don't agree with people who don't take drugs. There's more damage if you let those chemicals rot through your brain. Taking something is really archaic and so is chemotherapy, but I wouldn't say don't take that."
In her book, the comedian recounts a recent episode where she, once again, found herself at the foothills of a depressive bout. She types, word for word, how she was feeling at that precise moment, giving a rare insight into mental turmoil.
Equipped with the various techniques, does she have more fight against a potential relapse?
"There's no fight – it's just knowing how to shut off the lights and waiting until the cortisol comes down," she explains. "I knew what to do. I checked into a £29-per-night hotel-type place for four days. I didn't have to talk to anyone there. That's what I do now. And after that, I was the life of the party."
The passion in her voice is undeniable. There are plans for another book. And she's going back on the road soon with 'Losing It', taking a residency at UCLA in California, where she will hold weekly forums.
But there are still many mountains to climb.
"I've only just started," Wax laughs wearily. "We need to get books like 'The Secret' and 'Tickle Your Inner Child' off the shelf and get books about how your brain works on.
"And what I ultimately want to establish are walk-in centres for mental illness, which is what I would have killed for when I was younger. If a pack of drunks can organise something as wonderful as that, why can't we?"
'Sane New World' is out now