I hear you! Just finished (I hope!) a two-month stretch of dumping nearly 100 'standard' rating points here.
For me, it's simply getting careless and stale. Too much internet chess = growing superficiality and carelessness = absolutely silly blunders. I don't think this applies as much to otb chess. It wasn't my experience, anyway, and I think that was due to playing only 50 or so otb games a year: each game is 'valuable,' and you don't want to squander it.
I don't do otb anymore, just here, mostly 'standard.' I'm trying to concentrate on blunderchecking, on looking at every check and capture, etc. --looking at the game with beginner's eyes. And limiting playing to one or two games a day.
Every now and again I'm afflicted with a medical malady that I've coined "stupid brains". It's where you fall for every trap, miss every mating move, leave pieces hanging, and generally blunder your way through games in the most frustrating and appalling ways possible. After about a week of playing quite well(I'm not exactly magnus carlson but I did manage to beat a +2100 player in an unrated blitz game) I went on a 10 game losing streak and have just been playing horribly for the past few days. So I ask you the chess community what is it that you do when your mind gets cloudy and just can't seem to bring it all together anymore? Do you try to play through it? Or do you take it as a sign that you need to get away and clear your head, possibly go for a walk or read a book? Or do you think these are just unavoidable phases that you can't really do anything about other than wait for them to pass?