How Do You Feel When You Finish A Book?

This is how Roald Dahl's grand-daughter widow remembers him feeling:

He used to get grumpy when he was finishing a book and I remember saying, "But you should be so pleased you're reaching the end!" And he used to say, "You don't understand - it's the fear of never writing another one."

(Edited to correct grand-daughter to widow--I misread the preceding paragraph.)