What must a patient do if he feels anxious or gets a panic attack due to irregular heart rate?

Hello doctor,

I am a 37-year-old female and have been experiencing episodes of fast heart rate for the past four weeks. It happens suddenly, and my heart rate goes up to 165 beats per minute. I have consulted my doctor twice, but he thinks it is anxiety and gave me the tablet Propranolol 80 mg and asked me to take it daily. When I take the tablet, my heart rate becomes alright, and I feel calm. I am scared that it is something serious. I had undergone an echocardiogram twice the last year, which was normal. The cardiologist told me not to worry as my reports had no problem. I am a very anxious person and remain worried all the time. Would the echocardiogram report show any change if something goes wrong with my heart rate? I am going out of my mind and afraid to live my life. I was taking my daughter to school today, and my heart started racing. So, I took the tablet Propranolol 40 mg, but my heart rate was becoming irregular. I am honestly terrified about my heart problem. I experience shakiness, dizziness, and dryness of the mouth. I have had a complete blood count test done, but my blood reports and blood pressure are normal. Please help me. Thank you.

Thank you doctor for the reply,

I had panic attacks and unpleasant feelings in my stomach all the time. I have just been diagnosed with multiple sclerosis, and my son has been diagnosed with autism. My eldest daughter is suffering from severe mental health problems. I honestly have a nervous wreck, and I cannot control it. I get terrified when my heart rate goes up to 165 beats per minute because I feel I will suffer from a heart attack or stroke. My doctor told me my pulse rate is fast but regular. Today I took the tablet Propranolol 40 mg in the morning. Please suggest when to take modified slow-release Propranolol 80 mg capsules?