In less skilful hands the symptoms of bi-polarism, a condition many struggle to understand, could make for a depressing read. But London-born Forrest, who was a Sunday Times columnist by the time she turned 16, has turned her suffering into a witty, wise and well-observed page-turner that is bursting with emotion.
Forrest's book has had a lot of good reviews which have put a spring in her red-sneaker steps, though there are detractors who have described her as a "self-obsessed attention-seeker."
"The world has to describe my book the way they want to," she says. "Some read it as a love letter to a lover. Others as a love letter to the doctor or to my parents. They are three very different kinds of love. But what's really hard to take is the view that it's a kiss-and-tell book."
To describe the memoir as a "kiss-and-tell" is indeed wide of the mark. The tabloid tradition is for the teller to name the kisser and Forrest only refers to her lover - "the movie star with the storied reputation" - by the initials "GH", short for "Gypsy Husband". Having predictably googled Forrest before our meeting and seen photographs of her looking happy, holding hands with former hell-raising actor Colin Farrell in gypsy guise, I assume he is the "GH" in the book.
"Everyone thinks they know it's him, but I have had a lot of boyfriends who were actors," says Forrest, who also documents her relationship with an award-winning writer in the memoir without identifying him. "Anyone who buys this looking for a kiss-and-tell will be disappointed. The men in it are almost all anonymous, but I gave them the heads up that I was writing it and the opportunity of a vetting process. One of them actually wanted me to put his name in it he liked it so much." For the record that was not Colin Farrell, though he told Forrest to go right ahead.
"That's the thing about actors," she says thoughtfully. "They can't help thinking: 'If I'm a piece of s***, how can it be I'm the centre of the world?'"
Forrest grew up in west London with her younger sister, Lisa, in what she describes as a loving and supportive Jewish family, albeit a bit unusual. She cites examples of her father, Jeffrey, a solicitor, writing her an excuse note for gym in a perfect triangle which infuriated the teacher, and her mother Judith, a writer, perpetually talking to herself in the kitchen. Even her sister's imaginary childhood friend was on the run for drowning six kids.
As Forrest herself observes: "Perhaps because my family are how they are, it took a little while to realise -settled in Manhattan at the age 22 on contract to the Guardian and about to have my first novel published - that my quirks had gone beyond eccentricity to those cold, deep patches of sea where people lose their lives."
It was in her early twenties that she attempted suicide, though she first considered it when she was 13 and took Valium in the family bathroom. She then spat out the pills and went down for dinner.
It was at this time that she also interviewed Nigella Lawson for her school paper and so impressed the celebrity chef that she recommended her to the Evening Standard. Forrest did not look back career-wise - as well as the Guardian, she has written for Vogue, Harpers Bazaar, and many other magazines - but privately she was always looking inwards.
Her mental problems led to self-harming, the scars of which are
visible on her arms, and there are more, she tells me, hidden from view on her neck, legs and stomach. It is not for nothing that as a music journalist for the Sunday Times, she found she had more in common with the damaged artists than her colleagues. "I was also befriended by older women who were incredibly supportive and unusually wanted the best for me," she says, name-checking Julie Burchill who is still a friend. (Forrest, like Burchill, is former regular columnist for the JC.)
For all her success, she was deeply unhappy until she got to New York and met "Dr R" (Dr Jeffrey Rosecan) who taught her about "pattern breaking" over the eight years she was his patient. It was in fact the most significant relationship in Forrest's life until his premature and unexpected death from cancer.
"Everyone should have access to therapy," she says. "I don't see it as a bad thing. It's the same as having a personal trainer, but cerebral. It's part of human maintenance."
Perhaps the most interesting and significant thing about the book for JC readers are the constant references to Judaism by this author who admits to having no religious upbringing. "My parents were actually suspicious of me becoming religious," she says, and were probably amazed to find an entire chapter dedicated to a sermon given by Rabbi David Wolpe of the Sinai Synagogue in Los Angeles. "The rabbi had seen me crying in shul, so he knew me," she says. "The one thing I've liked about myself consistently is being Jewish. I love the fact that our religion allows us to question and challenge everything."
Her latest personal challenge is completing a screenplay about the life of New York punk icon Debbie Harry. "The ultimate shiksa goddess is my working title," laughs Forrest who has even found herself a nice Jewish boyfriend to live with.
"He is a writer," she adds. "And yes, he has read the book. I told him everything, so he didn't have to google me."
