I know the feeling!

Though, I started recently to have less of it. I started reading for things I need to read on my standing desk, which makes it much easier to actually move in process of reading, which my brain happier, apparently. Also, I can just jump on and off reading in progress (and walk around room), with same result. Definitely recommend using a standing desk in such a way, if you have trouble focusing on reading that you have to do.