I totally agree with Tom - same thing happened with me from age 9 until I was 42.
I had hr's in the 200's back to back pvc's long qt's; fainting episodes and some other things on Ekg's when I complained of my heart flip flopping out of my chest and my primary said "you're fine" for so long I believed it - they tried the anxiety cop out with me also but I wouldn't take meds
I would send a written request for his test results or find a good cardiologist and have the dr forward his test results to the cardio and at least have a preliminary checkup just to make sure
This is quite often the diagnosis when a GP administers an EKG and looks at the perfectly normal looking trace. "Looks fine.....you're having anxiety", prescribes medication that's not really required, and you've still got the problem. What you could be experiencing could be any one of a number of paroxysmal cardiac events; multiple PVC events, VT, SVT. Once these pass, your heart settles down, and appears normal.
I've gone thru the same scenario, even being questioned by a cardiologist as to whether I dabbled in drugs at all. After all, how could a 35 year old man with a background of competitive athletics have a faulty heart? I had nearly a lifetime of these events, and just persevered. The only doctors that actually saw the event were when I was six years old, then again at 21 when I had a cardiac catheterization at Deborah Heart Hospital. I never got sent down the "anxiety route" because I gave the physicians a detailed description of what I was experiencing. I carefully described the feeling, timed my pulse, wrote down how it started and how it finally went away, and what I did to make it go away. (I was taught a method at six that I used my entire life). I just didn't tell them that I "palpatations". Holters always show nothing except an occasional PVC. In my late 50's, I finally encountered a cardiologist in a new area that I had moved to that listened to my story, and decided to put me on a 30 day monitor, a simple device the one wears all the time except for showering. That little device changed my life. After capturing one event about out 2 weeks into the test. For the first time, I had a cardiologist call me late at night to check on my condition, and got the ball rolling towards a fix and a cure.
The point of all this is to tell you to not give up! Persevere, and don't except a diagnosis of anxiety. I can't imagine how many people are walking around with valid cardiac issues that are being medicated for anxiety problems. Keep on it and good luck.