Brain fog is typically a result of toxins accumulating in the brain most likely from the massive oxidation that the immune system creates. The immune system is likely being triggered by a pathogenic organism.
Reducing the amount of toxicity should free up the brain fog. Use of Vitamin C in copious amounts along with other antioxidants should help. I like some of the zeolite sprays, oral EDTA. Bulk charcoal has always worked wonders as well as chlorella.