I never know when I'm going to be in it out out of it. It's maddeningly random.
Except for a few short scenes and some word-changes here and there, I pretty much stopped making forward progress on my novel just before Worldcon of last year. Oh, I'd have days where it seemed like things were happening, but nothing much ever did.
I started doing some restructuring about a month ago, and liked what I saw. I've done more, and while I've thrown out about 10,000 words over the last two weeks, I've written about 15,000. And that "third act" (of a "four act") work that's been giving me nothing but headaches for over six months is finally falling into place.
I've also been sick now for nearly a week, with bronchitis (again) and I'm not sleeping. So the fact that I'm making any progress with anything right now is heartening, to say the least.
I even queried my second agent. I got turned down by one a while ago, decided to get more finished before querying again.