Anaphylaxis is a term used to describe sudden onset of severe, potentially life-threatening allergic reactions involving one or several body systems. Symptoms may include sudden onset of mouth or throat swelling, difficulty swallowing, trouble breathing, or wheezing. Gastrointestinal symptoms can include onset of sudden, severe nausea, vomiting, diarrhea along with lightheadedness and even passing out (symptoms of low blood pressure), with or without the breathing symptoms. Anaphylaxis can happen as a result of exposure to a medication (e.g. antibiotic), food (e.g. if a person is allergic to peanuts or tree nuts), or insect stings (e.g. bee stings or fire ant venom). Anaphylaxis is a medical emergency that requires immediate medical attention; people witnessing someone having this condition are advised to call 911 and stay close by until help arrives. If the person affected has a known allergic sensitivity and carries epinephrine (e.g. an EpiPen), it should be administered right away while waiting for emergency personnel.