Anaphylaxis causes the immune system to release a flood of chemicals that can cause you to go into shock — blood pressure drops suddenly and the airways narrow, blocking breathing. Signs and symptoms include a rapid, weak pulse; a skin rash; and nausea and vomiting. Signs and symptoms include: Skin reactions, including hives and itching and flushed or pale skin. Low blood pressure (hypotension) Constriction of the airways and a swollen tongue or throat, which can cause wheezing and trouble breathing. A weak and rapid pulse. Nausea, vomiting or diarrhea. Dizziness or fainting.