How do you know if you are having anaphylaxis?

Bad things happening. Anaphylaxis is a potentially life-ending allergic reaction. Parts of the body involved: skin, heart & respiratory & digestive systems. In anaphylaxis at least 2 are involved. Skin symptoms in 95% - hives, swelling of eyelids, lips, hands, feet or overall flushing. Falling blood pressure, fainting, difficulty breathing through throat or lungs, nausea, vomiting, diarrhea & sense of doom are others.
Anaphylaxis. Anaphylaxis is a severe, whole-body allergic reaction to a chemical that has become an allergen. After being exposed to a substance such as bee sting venom, the person's immune system becomes sensitized to it. When the person is exposed to that allergen again, an allergic reaction may occur. Anaphylaxis happens quickly after the exposure, is severe, and involves the whole body.