Heart pounding out of my chest continuously?!?

i don’t know why but for some reason, when I was trying to get to sleep, my heart started pounding out of my chest. I’ve had this for three days non-stop and i try to relax but my heart rate does not slow down. I have recently been to the doctors and they told me that my heart was quite fast. (i am only 16 btw) I had an ECG test and that also said that my heart was quite fast.. The doctor prescribed me with Propranolol which is supposed to reduce my heart rate and anxiety. i don’t know if it is anxiety that i am suffering with as my best friend just recently passed away but i would just like to know if it is anything serious.. i hope it’s not. Thanks

You should try to relax when n bed.

Social anxiety video I’m shy I can’t keep eye contact I am stupid I feel embarrassed I feel anxious