Writing books is intrinsically hard. It's just a lot of work. It's wonderful but you have to have a wide view. Once you start coning down to deal with separate sections that need extra citations and detail, you can lose track of the big picture. I've learned over the years to recognize that feeling and not freak about it. But it's still quite intense. Like driving through that tunnel in Switzerland—or the one from Lhasa airport to the highway by the Yellow River. It just goes on, and on, and on.
Thank goodness we have bodies. We can exercise and move and get the energy flowing out of our heads, where it settles into a gray fog if you're not careful. If Buddhism is correct and we have an after-death state such as the bardo, I'm not looking forward to the fact that it's disembodied.