Less commonly, urticaria may precede a severe allergic rection known as anaphylaxis. In anaphylaxis, there are hives and angioedema, difficulty in breathing, lightheadedness, rapid or irregular heartbeat, stomach cramps, nausea, vomiting, diarrhea. If left untreated, anaphylaxis can lead to shock, coma, cardiac or respiratory failure, asphyxiation and death.