Steve Pressfield has a great take on this, where he calls that inner war "resistance", and everyone that's ever tried to create anything knows it well. We've all had to fight it.

I write every day. I know Aaron Sorkin does not. Stephen King, he does. Orson Scott Card does not. Everyone is different. For me, though, I'm right there with your post--if I don't write every day, it's a new struggle to start again, as if I hadn't been doing the work for half a decade. It was too much the first time; I'm not doing it again.

Can't wait for part 2.