By the time she was 33, Julia had decided that the only way she could stay safe was to barricade herself, and her moods, inside her new house. This, she decided, would be the place where she could hide and survive and live for ever.

The psychiatric world could offer Julia medication, and perhaps some cognitive therapy, to help manage and contain her illness. But management and containment were all that she could expect. She had long believed that her illness was a genetic bequest from relatives and ancestors, that it had always been inside her.

As far back as childhood, she could recall the "two Julias" - one dazzling and confident, the other convoluted and obscure. Leaving home at 18, the parallel versions of herself seemed to detach and unravel. One version emerged in states of fiery euphoria, radiating beauty and sexual energy, disdainful of the grey, ordinary lives of other people. The other was its depressive shadow. She has a memory of herself as a student in Scotland, riding along the cliffs at night on her motorbike, stick-thin and covered with sores, consumed by a sense of her own hideousness.

The first big depression consigned her to a Priory hospital in London, the second to the more gothic Gartnavel in Glasgow. It was only after a third that the pattern became clear. She had developed a seasonal cycle: three months of mania, three months of depression and six months of relative sanity. To be told that she had bipolar disorder turned out to be both a relief and a life sentence. It meant it was not her fault, and that she could dedicate herself to controlling her psychic extremes. But with the diagnosis came a creeping realisation that the idea of control was an illusion. Less than 16% of manic depressives recover from their illness. Relationships wouldn't endure. The idea of children was unthinkable.

Julia's first bid for security was to buy a small flat in north London, above an empty cafe. But then, driven by a manic episode, she decided to open the cafe herself, cooking from her own stove. First the builders came, then the prostitutes, then the policemen. Business began to thrive. She got a council grant to do up the property and employed seven people.

It couldn't last. She sold the flat and cafe, and instead bought the big house where she would confine herself. She talked the bank into giving her a £300,000 mortgage, and did much of the work herself, laying on the charm at the builders' yard, sourcing cheap materials, putting on a new roof, renting out rooms. She became obsessed. This would be her castle. Inside its walls, she would protect the remnants of the princess inside her and hide away the witch.

"Which was interesting," she says now, "because the very place I was building as my security literally went up in flames."

Three years ago, on May 15, Julia gave a barbecue for her Polish builders. That night, feeling afraid, she let the dog sleep in her bed, which probably saved her life. At 1am she was woken by the dog licking her face. The house was filled with a terrifying, animal roar. Opening her bedroom door, Julia was hit by a blinding white light and punched to the ground by a backdraft. Rushing to the window, she realised it was stuck down with paint.

"I'm going to die in my own bedroom," she remembers thinking, "aged 31, having achieved none of my dreams. No one is going to come. I am completely alone."

With a final effort, Julia forced open the window and crawled on to the ledge. Gasping for air, three floors up in a flimsy nightie, she watched people gather below. At least she was wearing knickers, she thought, as she clung to her dog and waited for the firemen.

In the weeks afterwards, Julia experienced what she describes as "total grief", plunging into a depression that was also ravaged by post-traumatic symptoms: nightmares, flashbacks, visions of burning alive. And then it struck her. She'd been reading a Buddhist book on the night of the fire, and an idea from it came back to her: impermanence. Everything is ephemeral. No one can expect happiness. Stop searching.

"It's hard to explain," she says. "But that was my turning point."

Among everything that had burned up was Julia's medication, and she hasn't taken any since. Perhaps the fire brought on a trauma in reverse - what specialists sometimes refer to, half-jokingly, as "post-traumatic growth".

But there is no straightforward psychiatric explanation for why Julia's illness has left her. She tells her story while breastfeeding her one-year-old boy, Ewen. Little Ewen's hair is flame-red, and Julia thinks maybe she'll get hers dyed to match it.

· Names and details have been changed.