Yes. Can really relate to exactly how you put it too -- though I often don't get a paragraph in before that happens. Eyes will be moving, then it'll occur that I have absolutely no idea what's going on. Just letters on a page.

Or I'll find I've read the first sentence over and over. Catching this, if I try really hard to make it through the paragraph, I can get "on location". If not, I simply give it up for another time.

Depends not just on mental state, but material of course. Sometimes, I just can't read at all. Other times, light and short, other times medium. I've just begun an epically silly undertaking -- a Russian novel from mid 1800s. It's going to be a looong haul, lol. Hey, 12 pages so far! (of 400) Let's pretend I'm going to make it, ok? )

For making it better, getting your rest and stress under control can never hurt. I think it's probably also useful to adjust your expectations to reading what you can at a given time and not beating yourself up if it's not where you think it "should" be. Because that just makes stress over it.