Anaphylaxis is an exaggerated immune response to a substance that can affect multiple organ systems. It is a diffuse, severe reaction that occurs rapidly upon exposure to an antigen. Symptoms may include hives, swelling, difficulty breathing, low blood pressure, nausea and more. Treatment involves administering epinephrine to reverse the reaction, maintaining an open airway, and stabilizing cardiovascular function. Patients experiencing anaphylaxis require rapid transport to a hospital for further treatment and monitoring, as their condition can deteriorate quickly.