Hi, The extremely severe allergic reaction, which is called anaphylaxis, can cause palpitation, chest tightness, shortness of breath, diarrhea, cold extremities. It is a medical emergency and treated with an injection of epinephrine followed by steroids. If your doctor suspected you had an anaphylaxis reaction, he would have given you an epi-pen for future episodes. I personally believe that you are not experiencing an anaphylaxis reaction. Your symptoms could be due to the side effects of the steroid medication you were given for your allergic reaction. Steroid medication can cause gastrointestinal side effects, and your symptoms of chest tightness and rapid heart feeling could be due to acid reflux exacerbated by steroid medication. They can also make you feel anxious and weak. I would recommend waiting till you are finished with your steroid medication. If your symptoms do not resolve, then I would recommend seeing a doctor again. Meanwhile, you can try taking over the counter antacids and see if they make any change in your symptoms. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Saralkumar R. Desai, General & Family Physician