I have chronic sinusitus (sphenoid) as well as my CFS which causes brain fog (albeit differently to CFS). This might sound a stupid/gross question but ... why does my sinus type brain fog disappear when my sinuses are dripping down my throat ? When they stop dripping (like when I take anything with an antihistamine which dries them up) the fog is back and I feel blurry and unable to concentrate. My sinuses have been especially bad since the flu over Christmas. Thanks for help you may have .