Terry Pratchett released this letter via http://www.paulkidby.com:
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 :o)
I felt my heart sank when I read about Pratchett's Alzheimer's. Pratchett is one of those authors that has never failed to entertain me with his books. I have read most of the Discworld series (I've stopped around Fifth Elephant, but I'm hooked on the Tiffany Aching series). I've loved his acerbic sense of humour that show us truthfully as the absurd creatures of whims and desires that we are.
Pratchett reminds us this letter is like Granny Weatherwax with her "I aten't dead" sign. He still has a few books left in him yet, he tells us -- he's not yet ready to surrender.