Talk to Endocrinologist on Rapid Heartbeat

I was diagnosed with hyperthyroidism in 2017, and doctor gave Neo-Mercazole for thyroid and Inderal because my heartbeat used to erratically become rapid and BP would drop. After two years and six month gap and test, Neo Mercazole was stopped and Inderal was suggested only when heartbeat becomes rapid. I didn't need it but since a week, my BP is dropping and heart beat is going upto a hundred without any physical activity, Inderal isn't affecting like it used to. Doctor isn't available due to situation. What could be the possible cause?