It's normal. If you're like me (and a number of others I know) you have cycles of low motivation and cycles of high motivation. Also, if you've just come off the back of an intensive period you will experience a very flat period for a short while. You will come out of it. The trick is keep things ticking over, perhaps do something mundane for awhile to relax your brain (or take a holiday). Just accept it's normal for now (it'll take the pressure off) and have some chill out time.