Patrick Cockburn: I hoped my son would recover soon. He did not

The illness struck with terrifying rapidity over the course of a few weeks

At the time my son Henry was diagnosed as having schizophrenia early in 2002, I knew very little about the illness. Almost the only thing I did know was that it did not mean having a split personality.

Sitting in my hotel room in Brighton, where Henry was in a clinic, I spent hours at my laptop finding out as much as I could about the illness. I was dismayed to discover that an eminent American doctor had said that what cancer was to physical medicine, schizophrenia was to mental illness.

I had already seen its shattering impact. Henry was a talented, prize-winning artist before he became ill and the illness struck with terrifying rapidity over the course of a few weeks, though Henry later explained to me how it had gestated over a much longer period. The first sign that something was wrong came, in retrospect, when I noticed during a visit to Venice in the summer of 2001 that Henry, who had always drawn quickly and fluently, was having difficulty in sketching the human figure.

In January 2002 Henry started going barefoot and adopted a vegan diet, which might have been student eccentricity. But he also began to fear mobile phones, clocks and even Brighton's green-and-white taxis. He climbed up a high wall at Brighton station and passers-by called the police, who asked him if he had seen visions. Henry said he had not, though he later told me that he had seen a golden Buddha, though only for an instant, as he sat on Brighton beach. Later he watched a tree move its branches and speak to him.

Finally, on 9 February, Henry had set off for his home in Canterbury, walking barefoot along the foreshore until he got to Newhaven, where he swam the near freezing water of the estuary. Picked up by fishermen who feared he was suffering from hypothermia, he was taken in an ambulance to Brighton hospital. I was in Afghanistan at the time and rushed back to see him.

I was told early on by doctors that one-third of people diagnosed as having schizophrenia have only one attack and recover; one-third have recurrent attacks but eventually show signs of recovery; and one-third never get better. In fact it is more complicated than that, but at first I hoped Henry would be one of the lucky third who recover fully.

This did not happen. Often Henry seemed to disappear into his own world of dreams and nightmares. Over the last year or 18 months he seems to be more in control, referring to what he calls his "polka-dot days" when voices and visions briefly return. He finds these painful and calls them "the torments", though he shows great courage in sustaining these agonies.

When Henry and I both wrote about what happened to him last September, I was struck by how many people wrote intelligent and touching letters to me about this cruellest of illnesses. It struck me also that its treatment, and the treatment of other mental illnesses, were about at the stage that treatment of physical illnesses had reached a century ago.

The causes of schizophrenia are suspected, but not known for certain. There are medications which control but do not cure it. Studies seem to bring understanding of the illness closer, only for others to disprove or qualify their results. Progress has been very slow.

Patrick and Henry Cockburn are writing a book about Henry's experiences, to be published in 2010