If not, I will simply put the story aside. Unfortunately, that's resulted in some of my books/series being incomplete and require me to come back to them, so I do my best not to leave them alone for too long.
As for those books that flow seamlessly and I can stay on task, I write several chapters, sometimes up to seven or so. Then I reread the book from the beginning. Updates, changes, modifications. Next seven or so chapters. Reread from the beginning. On and on I go. So, I rarely have a first draft because I update drafts throughout the book. That means when I'm writing the very last sentence, it's final. Once I read back through it, of course.
That's when I realize the dreaded anxiety hits me. I've finished the book. Done. Complete. Time for the next phase.
Now I'm overwhelmed and shaking because I know it won't be much longer before you've got the book in your hands. Now comes the constant doubt because I want you to love the book as much as I do and I immediately start thinking about what your reaction might be. Will you like the characters? Are they annoying (unnecessarily)? Are they likeable/unlikeable when they shouldn't be? Are they boring? Is there enough angst? Too much angst? Enough heat? Too much heat?