Hi, welcome to the forum. Shortness of breath is a serious side effect. I experienced it myself from taking Compazine - it was frightening! I told my doctor about it, and was advised to immediately stop taking it. They also put in my file that I'm allergic to it, so I'll never be prescribed it again. I would say call your doctor right away and let them know that this is happening. They'll likely switch you to a different medication that doesn't cause a reaction like this. What medication is it that is causing this reaction?