Take note that palpitations are common in healthy hearts, especially as we age. They can be induced by stress, caffeine, foods we eat, medications, alcohol, hormone changes, etc. Its a DISGUSTING cycle because you get heart palpitations, therefore you get scared and anxious, which brings on short of breath and dizziness, which can be mistaken as a sign that something could be wrong with our hearts....oof!
So, have things checked out, make sure your heart is functioning normally. If so, have the doctor re-evaluate your xanax dosage.