I have had a very similar thing going on. Rapid onset of food "allergies" following an elimination diet. I had severe withdrawals from my offending foods during the elimination phase. As I tried to reintroduce foods, with each sensitive food, I had rapid onset of brain fog and anxiety. Now I know that what was happening was that my adrenals were so depleted that they did not produce enough cortisol to control the allergic reaction to these foods. I am also hypothyroid which contributes further to this problem. Hypothyroidism causes low stomach acidity which leads to undigested foods passing through your system which exacerbated the allergic reaction I had to the foods. As my adrenals recover, I find that my reactions to foods lessens in severity. The anxiety is gone and now I am left with brain fog. Mostly when my routine is disrupted, when I try new foods, when i wait too long to eat, and when I'm under stress or don't get enough sleep. I take licorice root extract which helps maintain higher levels of cortisol in the body and just started a homeopathic for the adrenals too. I'm on tons of supplements the most important being b complex and vit c for the adrenals and chromium for my hypoglycemia. I also do bioidentical progesterone to support my adrenals. And I'm only working a four day week right now so I can get extra sleep and rest the other days. I limit my exposure to energy draining people and have learned to set boundaries and speak up for myself. It's been 9 months now and I can finally see an end in sight. I still have my bad days but it's always getting better.