Something strange started happening to me around 10 years ago. My shoe size grew from 9 to 11, my income permanently dried up, and the girlfriend I was going to marry left after we stopped having sex. It wasn't just the sex, or lack of it. I also dramatically changed, both personally and physically. My nose grew bigger, my forehead enlarged, and my face and hands became puffy and coarse. But these were all gradual changes that I only realised in retrospect. Some friends noticed more acutely. One, who hadn't seen me for four years, looked shocked when I opened my front door. “You've rearranged your face,” he blurted. My younger sister was blunter. She said I looked like I'd been in a fight.

I went from being dynamic and creative to someone who was apathetic and exhausted. My moods became widely variable. I was more anxious and easily fatigued. Inexplicably, my voice grew deeper. On many nights I had weird, out of body experiences. I woke up sweating, scared, and gasping.

I had been a successful freelance journalist and film maker, but things began to go wrong. Increasingly I went to the office late or not at all. Frequently I did little or nothing at work. Then I'd go home and do nothing there. Often I fell asleep at inappropriate times—at my desk or in the middle of having a cup of tea. Sometimes I tried hard to snap out of it by starting a grand new project, but it didn't work. I soon ran out of steam and mourned the loss of my former vibrant self.

From 1997 to the summer of 2001, …