From a Washington Post story by Karen Heller headlined “What scares master of suspense Dean Koontz? Plenty.”:

Few American writers sell as many books, live better or worry more than Dean Koontz.
“There are days that you think, ‘I can’t do this anymore,’” says Koontz, 77, author of more than 110 books that have sold over 500 million copies in 38 languages. “Of all the writers I’ve ever known, I have more self-doubt. I’m eaten by it all the time.”

Fears? He has a few.