Generally, anaphylaxis is a potentially deadly condition that results from an allergic response to a food or insect bite. However, there's also a type of anaphylaxis that results from physical exertion, like exercise. It's a rare condition, and it hardly ever causes death. The symptoms of exercise-induced anaphylaxis are similar to those of allergy-induced anaphylaxis: hives, swelling, constricted airways that lead to difficulty breathing, a drastic drop in blood pressure, nausea, dizziness or loss of consciousness. The exertion required to bring about anaphylaxis can range from jogging or running to dancing or playing volleyball. Even light yard work has been known to bring on anaphylaxis. The symptoms can last from a half-hour to four hours after you stop working out.
It's often hard to diagnose exercise-induced anaphylaxis, since symptoms vary from person to person and episodes aren't predictable. You might be able to exercise 20 times without incident, but then go into anaphylactic shock on the 21st time.