Increased Heartbeat, Numbness In Arm, Chest Pain. Burning Sensation In Pulse. What Should Be Checked?

Hi, on december 26, I was sitting watching tv. My heart started pounding and a wave of anxiety came over me which soon followed with numbess in left arm. Check blood pressure and it was 154 over 84. Passed after about 3 hours and I was ok. Until about a week and a half later it happened again. I was ok for a couple of days, however I started to get one or two of the symptoms everyday every 2 hours, then they would go away for a couple hours. Some days I feel fine, but recently they have been getting worse and more frequent. Mostly, heart pounding/racing with chest pain . Today however, my heart was pounding harder than it ever has and my jugular viens were pounging and I could almost feel a burning sensation pulsating with my pulse(if that makes sense. Ive been to the doctor, blood work, ekg , and echocardiogram came back fine and Im awaiting results for a 24 hour urine test for a pheochromocytoma . They gave me xanax for the time being to calm me down/ see if it is anxiety related, but I am not stressed out about anything and the xanax didnt seem to help today(first time trying it). SOmetimes I get wierd pains in my abdomen too. The pain in my chest is almost like a stabbing/needle pain. Do you know any possible things this could be/things I should ask my doctor to check? PS I did take vitamin B12 supplements for about 3 days before the all started to happen on the 26th and I do think I have gluten allergies but I have not been tested(sometimes I still eat gluten too). Im a competitive runner in great shape( have not been running due to my current condition though) so I would not think it was due to an unhealthy lifestyle. Thank you