Hi Brandibrat -- our Jon had an allergic reaction to Lamictal several years ago (the skin rash, vomiting, etc.), but that didn't seem to precipitate any other allergies at that time.
6 months after the Lamital reaction, he started waking up covered in hives. He hadn't been eating any new foods, and his only med was Depakote, which he'd been on for 6 months (it replaced the Lamictal), and isn't one of those drugs that typically cause an allergic reaction. His pediatrician thought it was the Depakote, but his neurologist thought it wasn't. Anyway, he was put on Claritin for a couple weeks, and that was the end of the hives (never did find what was triggering them). That allergic episode didn't seem to have any correlation with seizures (he'd been seizure free for several months on the Ketogenic diet at that point).
Tattoofriend -- eliminating certain foods (especially gluten, and also foods containing MSG) have helped with seizure control for lots of people. So...sometimes, some sort of food intolerance can trigger seizures. But it seems the opposite can also be true.
Our Jon was already gluten free (in fact, no grains at all) on the Ketogenic diet, but was eating eggs just about every morning for breakfast with no problem (and also eating avocado almost every day and eggplant maybe two or three times a month). Then, the eggs and avocado suddenly started giving him diarrhea, and the eggplant actually triggered seizures (he had 3 episodes where he had a seizure just after eating eggplant).
So, he's been off of eggs and avocado for about 4 or 5 months now, and we took out all the nightshade veggies (I probably will never give him eggplant again). We've been trying to reintroduce egg to see if he can tolerate it now.