I had this for a few years and it was scary. Couldn't focus, couldn't recall names for shit, and it always felt like my brain was stuffed with cotton. I went to numerous doctors in a quest to figure out what was wrong, but most blamed lifestyle or getting older and didn't take it seriously. It co-existed with constant fatigue, poor sleep quality, and diarrhea. It ironically cleared up after I had an attack of diverticulitis and they put me on some hardcore antibiotics and antifungals. It's assumed that I had a long term simmering gut infection and/or yeast overgrowth, because after the drug regime my stools became normal, dark circles under eyes lessened, and I could actually think again.. I would start off with some quality probiotics and reducing carb intake, and if it doesn't get better go to the doc and see if you can get something for gut yeast overgrowth.