Question: Very high HR episodes :

So I am a 23 year old med student. For the past 4 months ive been experiencing random episodes of sinus tach as well as several panic attacks. The latter seems to be preceded by cognitions (fear), sensations, and what you might call "cues" that trigger anxiety attacks. The former seems to come out of the blue, sometimes waking me up. Ive checked my pulse during these episodes on a pulse oximeter and it can get as high as 180bpm for very short periods of time, gradually slowing back to NSR (does respond to valsalva-like maneauvers). No dyspnea, chest pain, or syncope during episodes. Ive had several resting ECGs following these incidents which are unremarkable. Ive had an unremarkable stress echocardiogram (54% EF incr. to 68% upon exertion) with no exercise-induced dysrhythmia, dyspnea, syncope or chest pain. Ive had a normal 24-hr Holter study. TSH level is normal, as are my basic electrolytes + magnesium (immediately following episodes). 24-hour urinary metanephrine study unremarkable. Chest x-ray normal. Event monitor captured one of these episodes. Stach as high as 170. This was just 1 episode, though. Another (non-captured) incident it got over 180 and I called the paramedics, who took it and it was back down to 120-130 within 5 minutes.

My fear is that there is something other than anxiety, as I didn't think your own catecholamines could cause such a high HR. Also wonder if prior to event monitoring I could be experiencing some SVT runs, although ive been told SVT wouldnt gradually dissipate back to NSR, but would come on & terminate quickly. T/F? The in and out sensation of being aware of my heart beat has also caused me to become neurotic about sudden cardiac death. Should i be concerned about this? I am adopted so I have no family history.

Also, I have been assured by some that my heart can "handle" the very high sinus tach for days if not months and that i need to stop checking my pulse and treat these like panic attacks. Is this true?