If you awaken and dread going to work on your current book, you’ve taken too long in writing it. Put it in a drawer and move on to another project. Perhaps if it gathers dust for a little while, you’ll be able to view it with renewed enthusiasm later. Writing should be a labour of love and discovery, not drudgery.
If, on the other hand, you’ve written a book in just a few days, you’ve done it too fast. Ease up on the gas. You’re missing too much of the scenery.