I have recently developed a similar problem (since getting married and starting medical school).  I know what you are going through.  These situations are really scary.  I experienced dizzy spells and at one point something that to me felt like a seizure.  This seizure like experience started with the trouble taking in a deep full satisfying breath and then persisted to a tingling sensation in my face that let to every muscle in my body contracting at the same time (this was every painful and scary).   I later learned that this experience was caused by a ca++ imbalance that was due to hyperventilation (possibly caused by anxiety).  I have also had a lot of test that have all come back normal and had a hard time accepting that this might only be anxiety, but I have worked on trying to manage my stress and have found relief.  During times of stress the symptoms return.  Try to relax and see if that helps the problem.  I would suggest starting this process by talking with a friend and building confidence concerning your health (meaning there is a good possibility you are totally healthy).  That seemed to work for me.