Thanks for choosing health care magic for posting your query.
Yes, you need to be concerned about your health. From the description that you have given, if your cardiologist feels that there is nothing serious then the complains can be due to anxiety
disorder. You need to see a psychiatrist
who can examine you in detail and advice you some relaxation techniques
and also prescribe you some medications for the anxiety issues.
Hope I have answered your query. I will be more than happy to help you if you need any further clarifications.
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Wish you a good health!