I would have liked to keep this one quiet for a little while, but because of upcoming conventions and of course the need to keep my publishers informed, it seems to me unfair to withhold the news. I have been diagnosed with a very rare form of early onset Alzheimer's, which lay behind this year's phantom "stroke".

We are taking it fairly philosophically down here and possibly with a mild optimism. For now work is continuing on the completion of Nation and the basic notes are already being laid down for Unseen Academicals. All other things being equal, I expect to meet most current and, as far as possible, future commitments but will discuss things with the various organisers. Frankly, I would prefer it if people kept things cheerful, because I think there's time for at least a few more books yet

Beloved science fiction and fantasy writer Terry Pratchett has terminal early-onset Alzheimer's. He's determined to have the option of choosing the time and place of his death, rather than enduring the potentially horrific drawn-out death that Alzheimer's sometimes brings. But Britain bans assisted suicide, and Pratchett is campaigning to have the law changed. As part of this, he has visited Switzerland's Dignitas clinic, an assisted suicide facility, with a BBC camera crew, as part of a documentary will include Britain's first televised suicide. Pratchett took home Dignitas's assisted suicide consent forms.

He said: "The only thing stopping me [signing them] is that I have made this film and I have a bloody book to finish."

But he stressed that he was as yet still undecided whether he would eventually take his own life.

He said he changed his mind "every two minutes" but added that if he did choose to die would prefer to do so in England and in the sunshine.

Sir Terry, creator of the Discworld novels, was 60 when he was diagnosed with terminal condition and has since campaigned passionately for a change in the law to allow assisted suicide in Britain.