If you have been evaluated by a cardiologist and an endocrinologist, they have probably eliminated all the possible causes that could endanger your health. This does not mean that the problem is not real, only that it is not dangerous. My best recommendation would be to ask your primary care doctor to try and find a medication that helps the symptoms--a change in beta blocker sometimes works, also some of the anti-anxiety medicines are effective. My sympathy on all the discomfort--keep trying and there's a good chance that something will work.
Eva F. Briggs, M.D.
Online Expert
James Hubbard's My Family Doctor