Can regular fasting trigger allergies?

I've been on the IF train on and off for about two years now, doing 18:6 most days and 14:10 on days that I feel physical instead of emotional/psychological hunger. It's definitely shown nice results, but lately I'm noticing changes in my appetite. I never seem to get hungry, once going close to 24 hours without a single pang because no non-fast food options were available. I mostly eat now out of a sense of duty to my body, and feel cravings when I'm stressed/overwhelmed, but otherwise no real instinct to eat. I've also started getting sick after eating carb-heavy meals, especially when eating out. Had some gluten-free pasta at a pizza express the other day and felt like shite the rest of the day and most of the next. It was a little worrying how my mood seemed to drop, - physical strength and energy seemed okayish if not very high, but I felt very depressed, lethargic and congested. Almost like I was coming down with a flu. I have no known food allergies and this is a recent development, so I'm not sure if I should be worried or it's just a series of flukes. Should I be concerned or is this par for the course?