I am going to tell you about the worst thing that ever happened to me. Think of the most wretched day of your life: maybe it's when somebody you loved died, or when you were badly hurt in an accident, or a day when you were so terrified you could scarcely bear it. Imagine 4,000 of those days, together in a big chunk, and you're getting close.
I'll tell you of something I saw in a prison called Bang Kwang, nine years into my imprisonment in Thailand. This isn't an isolated incident - it's one of many - but it is one that stays in my head and plays like a short horror movie, over and over.
I was awakened late one night by the screaming of a young French prisoner in the cell next door. The sound of his scream was excruciating. It wasn't just a scream of pain but of madness, too. It was the sort of sound you would never want to hear coming from a human being.
For hours and hours he screamed, until I and a friend called David, who was in a cell opposite, began screaming back, begging him to tell us what was wrong.
Eventually David and I began shouting for the guard. We pleaded with him to let us into the Frenchman's cell to see what was wrong.
When we entered the cell, the Frenchman was alone, curled into a ball, facing the corner. His screams didn't stop for the whole time we were there: he seemed totally oblivious to our presence. As soon as we turned him over, we saw what was wrong.
On his neck, just below the ear, was an enormous lump, about the size of an avocado. As we looked at this lump, it appeared to be moving.