Heart problems or anxiety? Mom's 73...

Hi, my mom who's 73 y/o complained of heart palpitations (no chest pain or shortness of breath) and extreme fatigue about 3 mths ago. She was hospitalised for 3 days during which doctor ran tests on thyroid, blood, ECG and blood pressure. The results all came back normal. She was prescribed multi vitamins upon discharge. However, she still experiences heart palpitations, fatigue (even when resting just sitting down watching tv) and worse of all, she now suffers from insomnia. She started taking sleeping pills but still feels unwell. Further tests like 24 hour Holter monitoring and ultrasound of the heart were conducted but results still came back normal. Her cardiologist thinks she has depression/anxiety and wanted her to see a psychiatrist but my mother insists she is not depressed. So the doctor referred her to see a geriatrician next week. My concern is whether the doctor has misdiagnosed her and what is really wrong with her? I am most worried doctor might have missed out something. Please help, thank you.