Probably totally irrelevant, but I used to get horrendous wipe out brain foggy tiredness pre-coeliac diagnosis - always after eating protein (but sometimes at other times). I had it explained to me as resulting from leaky gut - protein molecules weren't getting broken down in my gut properly (right down to amino acids) because of the coeliac damage which meant that slightly bigger molecules were getting into my blood stream. Some of these breakdown products had some similarity to sedating things, so when it hit my poor braincells I was out for the count. It was funny though that if I kept doing physical things I was fine. The moment I stopped I'd be asleep. It was hard to understand how I could walk several miles and feel absolutely fine, then totally wipe out the moment I stopped.