What do you advise if i'm newly allergic to nuts but forgot and ate a banana walnut muffin. difference since the nuts were baked?

Food allergy: By the time you post the question, I assume it has been several hours since you ate banana walnut muffin. Food allergy reaction occurs within seconds to minutes but sometimes can delay up to 8 hours after eating the food. If you don't have any reactions, you don't have walnut allergy. Remember a positive allergy test to food does not always mean you have food allergy. See a well trained allergist.