Completely clogged up after eating filberts; it's like my hazelnut allergy?

Same nut. Hazelnut and filbert sometimes refer to the exact same nut (corylus avellana) but sometimes filbert refers to a closely related species (corylus maxima). Either way, from an allergy point of view they are essentially the same nut and if you are allergic to hazelnut you should avoid filbert and vice versa.