I’m assuming you’ve heard amazing statistics on this or you wouldn’t be asking. What you’ve heard is probably true, or close to it.
Robert Louis Stevenson, reportedly suffering from tuberculosis and on a six-day cocaine binge, wrote the classic Dr. Jekyll and Mr. Hyde in a frenzy.
His wife commented that it seemed unbelievable a man in his condition could have produced a work that long, 60,000 words—only a little shorter than most books, in six days.