Perhaps something like this has happened to you. Here's an annotated graph of what it's like to make a book, with 'joy' being the Y axis with time along the bottom (click to enlarge)…
2. The first trough of reality. Now that I've pitched the idea to someone (and I'm on the hook), the reality of what has to be done sets in precisely as the manic joy of invention disappears.
3. Wait! The epic pause of reality. It's not quite as bad as I feared. I can see a path here, maybe. I'm still in trouble, sure, but perhaps…
4. The horrible trough of stuckness. The path didn't work. The data isn't here. Critical people have said no. People in critical roles have said no. I can't find any magic. Sigh.
5. Flow. This is why we do it. The promises made as a result of #1 pushed me through the horrible trough, and the lights are coming on and my forward motion, my relentless forward motion, may just be contagious. Let's not talk about this, because I don't want it to dissipate.
6. The pre-publication lizard-brain second-guess. I see the notes that have come back to me, all that red pen, the not-quite-ebullient look on the face of a trusted reader. I am sniffing everywhere for clues of impending doom, and yes, there they are.
7. The realization that it's good enough. This is the local max, but not the universal one. Optimists welcome. It's not perfect, but it's going to ship, and good luck to it.
8. Post-partum ennui. "Why haven't you read my book yet?"
9. Life. And this is the long haul, the book in the world, the hearing about a book you wrote ten years ago that's still impacting people. The crepe paper grand opening bunting has been taken down and there is no one left to write a snarky review, because the book is on its own, touching, spreading and being.
And then, sometimes, #1 happens again. Or not.