Hello, i've been suffering from the several days-long episodes of brain fog or a cognitive shutdown for about 12 years now. it comes and goes without ?

Neuro-psych: Brain fog or cognitive shut down off ; on for 12 years need extensive , comprehensive neuro- psychiatric team of doctors evaluation. On line advice in this complex matter, is not possible. Please go to university research teaching hospital. Thanks.

Variety of causes: One can suffer from brain fog as you describe for many reasons including metabolic derangements, infectious, medication induced, aging, and psychological. The only way to definitively answer such a broad complaint is to be fully evaluated for all these conditions. Standard practice dictates ruling out all physical causes before ascribing psychological reasons to such symptoms. Feel better soon!

Gluten sensitive: You may try seeing your doctor and be tested for gluten sensitivity. Getting tested before starting the gluten free period is important.