Insect stings and food, to name a few.
I have really bad allergies. Oh, I'm sorry to hear that your immune system is hypersensitive to things that usually cause no problem for others. May I ask what you are allergic to? I am allergic to pollen and some dander. When it's pollen season my allergies go crazy. That's bad. Things like food and medications can cause severe reactions I didn't know you could be allergic to medicine. What else can people become allergic to?
Food, insect stings, and medications are common causes of severe reactions.