For me against brainfog helped Rhodiola Rosea (about 300mg a day). It was like a miracle, i couldnt concentrate before, but with Rhodiola, it helped A LOT. I work as a computer programmer so not being able to concentrate, and being all brain foggy all day, was a horror.
Also what helped me was eating almonds. Sounds easy but it really helped, and also avoid soy products and gluten.
Genereally, try to eat healthy, lower stress and try to relax your body more, this helped for me.
Maybe sometimes brainfog and derealization is a result of fear and anxiety. So probably getting a therapy or some other help to learn handle fear and anxiety could also help.