Screenwriting : Diagnosing Charles Dickens by Susan Holtzer

From Mental Floss: Dickens would start falling into depressions with the start of each new novel. The first one to cause him problems was one of his lesser-known works, The Chimes, in 1844. After that, Dickens’ friends wrote that he became down every time he set to work on a new project, but that his mood would gradually lift until he was in a kind of mania by the time he finished. That's the mental condition known as "being a writer."