Good grief! Mine is about 70% done, too. Is this the literary equivalent of a seven-year itch?

You're right, it's good to have something exciting to look forward to after the WIP is finished, and it's certainly good that the idea gets to stew and simmer in peace. I just wish it didn't have to happen at this particular stage! Or be so insistent. Sigh.
I doubt I'll be able to get any proper work done until this initial frenzy has spent itself, but I hope it won't take any more than a couple of days. That's about the length of most of my infatuations, anyway...
Glad to hear I'm not alone, though!