The facts are that the book was written, printed, revised, and ready for press in five weeks.
The manuscript of the book was complete within four weeks.

It possessed me.

I wrote night and day.

There were times when I went to bed and, unable to sleep, I would get up at two o'clock or three o'clock in the morning and write till breakfast time.

A couple of hours' walk after breakfast, and I would write again until nearly two o'clock.