I have this problem. I will just be sitting, driving, or anything and my heart rate
jumps to 290 bpm. I only know its this fast because of the heart monitors in the emergency room. It first happend when I was 20 I am 35 now and it became more frequent in the past 4 years. I had all the same test done that you have plus an EP Study. That is where they go in like a catherzation and study the electrical path of you heart. They found nothing. I had the same anxiety's that you have. Places I wouldnt drive because I swore it would make my heart race becuase I had had an attack there, and things I wouldnt do becuase I had an attack before doing it.
Once you stop worrying about it, it goes away. I know its hard to do, your heart starts racing you feel the beat in your throat. Your face starts sweeting, its hard to breath, and you cant feel your pulse. Its scary but you already know this. Its called V-tach by the way, and depending on which part of your heart it takes place it can be deadly. I know you didnt want to hear that. My cardiologist told me as long as Im not passing out not to worry about it. They wanted to put a defebulator in me, but I like to ride motorcycles and you cant do this.
I have had to be shocked back into normal rythm many time's. Have you gone through this yet? Dont worry they give you medicin and you dont remeber it.
There are somethings you can do. Dont drink caffine, too much sugar. get plenty of rest at night. And mostly dont let it control you. Tell yourself if it happens it happens, unless your passing out. I have started drinking sweat tea again with caffine and have been fine for along time. I used to keep track of how long I would go but after I stoped doing that I cant tell you when the last time I had an episode.
Good luck with it, and know your not alone with this. I have also found that during an attack if I lie on my stomach it goes away and somtimes on my left side. And take some deep breaths.