Sounds like stress to me. I have some downtime during December after getting my third book written. I tried to play some games, and take some time off with the holidays coming up but if I go more than a few hours, I end up feeling strange. Like I could be outlining the next book. Researching some ideas. Polishing a blurb, or learning about the changes HTML5 brings to the latest edition of Kindle Fire devices.

In other words, if I'm not working on my books, I am just wasting time.

I also found the joy of twich.tv. It's like football. I can just watch someone else play and not worry about not having the time to put into it to get my monies worth or getting a torn ACL out of it.