It seems everyone hits a plateau and even a dip...im my opinion...this happens right before a big increase...
However, GM Andy Soltis used to say that every chess player will reach their peak after 8 years of serious study. I don't know if I agree. I would take a day or two off and do something else. Then, I'd come back.
Yes I have been there and am experiencing something of a slump right now. I've always been a inconsistent player. Right now my rating is hovering around the lower part of 1600, and I'm getting creamed by 1500 players. My highest rating was the upper 1900's, which wasn't a fluke as I was beating players around that rating on a consistent basis. Some players fluxuate.
I can't give you advice, as I am there. It is weird. I'm not near as good as you, but consistently after 4000 games 1100 to 1200 player. I'm in a week of "weirdness". My score is in the 900's! I've tried studying it, but have never lost this many games.
I'm wondering if anyone has ever experienced a chess slump. I only recently started playing and have spent countless hours over the last 3 months reading and studying chess principles. My rating began to rise in concert with the time I was spending studying, but then I hit a "slump". I started to regress. Just wondering if this is common.