Authors who were clearly deranged lunatics

Calling at least several of the authors on that list 'deranged lunatics' is maybe stretching the boundaries of the term a bit. Tolstoi might better be described as a religious obsessive; Woolf and Hemingway both suffered from bouts of severe depression (that in both cases ended with their taking their own lives), but were quite lucid, functional and productive throughout much of their creative years, excepting some intervals. The same could be said of Plath. Poe was an alcoholic who likely suffered from depression and possibly other mental illness, but again was highly productive and rational enough to write a considerable body of work while struggling to keep the wolf from the door. P.K. Dick I confess to knowing little about as far as his mental state went, and I've read only a couple of his books; in the case of Swift, his 'madness' such as it was (it sounds closer to something resembling Alzheimer's, with violent manifestations), did not incapacitate him until much later in life, though some cite evidence of oncoming madness in some of his works, such as Gulliver's Travels.

Another writer who definitely suffered from mental illness (schizophrenia, to be precise) was Zelda Fitzgerald, wife of F. Scott. Under the shadow of her famous husband, her own writings--which show evidence of pretty considerable talent--were doomed to inattention during her life. Zelda's behaviors became increasingly erratic, culminating in confinement to an asylum for quite some time. Even after she was declared capable of living outside of an institution, she would still have to return for relapses of the illness. In fact, she was in confinement at the time of her death--during a fire at the mental hospital she was in, unable to escape and burning to death with several other patients trapped in a locked ward.