Most people go through life without ever experiencing anaphylaxis — a rare but severe allergic reaction that occurs suddenly and can be life threatening. Anaphylaxis can happen moments, or even seconds, after being exposed to a triggering substance. For example, you may experience anaphylaxis directly following an insect sting or a penicillin shot. Because an anaphylactic episode can progress quickly, it is important to know the warning signs and prepare for an emergency episode if you have had an episode in the past.

What Is anaphylaxis?
Emergency Treatment
Pinpointing the Anaphylactic Trigger
Idiopathic Anaphylaxis
What To Do If You Have Had an Anaphylactic Episode:
Source: American College of Allergy, Asthma and Immunology