sounds like
PVCs to me, when u take ur pulse do u feel a pulse, pulse, skipped beat, big pulse - that's many times a premature ventricular contx, i get them, i feel them in my throat, sometimes it feels like i'm going down in an elevator, or a bubble is traveling up my esophagus - my holter showed 107 of them in 24 hrs.
PVCs usually go away with increased heartrate which is prob why u don't feel them when working out,
PVCs r usually benign - but scary and anxiety brings them on like rocky V
u did the right thing with holter,
echo EKG - if still worried go to cardio for 2nd opinion - they make u feel better
but sounds benign or normal