Does your chess vision vary a lot?

I've been spending a lot of time with the Tactics Trainer lately, and I've noticed that my vision of the board seems to be really variable for no real reason. I'll get on a losing or winning streak and drop or gain hundreds of points in almost no time. Right now I'm sitting at 2031, but yesterday I dropped from 1850 to 1600 before climbing back up. At one point I was missing simple one movers and getting six problems in a row wrong.

Has anyone else noticed such big swings in board vision?

Yes, actually I seem to see the board very well when I had good rest, and I can even miss simple forks at night after a few hours of play, or when I'm tired. But since I'm not premium, I mostly train for tactics on another website (where the difficulty level is similar).

All the time. If I am fresh and sharp I do well. And If I'm tired or the least bit distracted, then I may miss four or five easy ones in a row. But I generally do tactics trainer late at night. Therefore my rating is not that good. But that doesn't matter, since it's all about pattern recognition.