Writing fiction is liberating. If you have spent much of your time composing work that demanded citations and providing lists of sources, suddenly not having to do so is a strange sensation. The page is yours entirely.
Characters may make false or stupid statements, or offer “insightful” and “correct” ones. Those one writes about become almost “real” to you. You outline their existences and set the parameters. They are fully your creations.
Building them and setting the scene, and doing so consistently and interestingly, is also incredibly hard work. I have a new respect for fiction authors.
In a sense, you are always working. If an idea popped into my mind, I would tap it quickly onto my iPad or iPhone, or scribble it on a piece of paper, to make fuller use of later. Regularly something appeared in my head at 4 AM, and I jumped up and threw it on the PC, terrified I would not remember it later.
I can understand far better now how relieved fiction authors are when they have finished their novels. Yet the moment you set it aside and say to yourself “Enough!”, what to do next hits you. If you are planning another novel on the same general subject and characters – which I am – the end of one book is really just a pause for breath.