Anaphylactic shock is a severe and potentially life-threatening allergic reaction that occurs when someone is exposed to an allergen, such as certain foods or insect stings. The immune system overreacts to the allergen, releasing chemicals that cause blood vessels to constrict and become leaky. This can lead to a rapid drop in blood pressure, difficulty breathing, swelling of the face and throat, dizziness, fainting, and even heart failure. Anaphylactic shock requires immediate medical attention and treatment with epinephrine (adrenaline) or other emergency medications to restore normal blood flow and prevent death.