Whenever I have a prolonged coughing episode (as in thick allergy phlegm), my chest breaks out in hives from the top of my breasts and the sternum to my collar bone. It also happens when I have had a vomiting episode with the flu. This didn't happen when I was younger. It stings and then itches for hours or even 'til the next day before settling down and going away. It seems to be connected somehow to not enough oxygen during these times. Can you explain the physiology?