In reply to OneLifeOneHeart:
I'm not going to say what, if anything, is wrong with you over the internet, because its just impossible to be in anyway accurate - and you have to realise that. However, marsbar raises a genuine possibility, and I'll enlighten that further with a personal anecdote. When I was in my later teens I started getting ectopic heart beats (basically a premature ventricular contraction followed by a compensatory pause). Sometimes they would occur every other beat, sometimes frequently and randomly, sometimes only sporadically, but whatever the case I found them deeply unnerving. Having seen a specialist and been noted to have small abortive runs of these beats (ventricular ectopics), I was offered a beta blocker, which I turned down. Incidentally, as an aside, I still wonder whether climbing may have caused these, in particular because of a bad tendency to breathhold (which appears to me to simulate a valsalvas manouever - see wiki) particularly when training on overhanging 30deg steep boards for power or power endurance and exacerbated by body tension (this is only a hypothesis). Anyway, alone at uni, I found it difficult to concentrate on work and difficult to sleep, because being skinny, I could always feel my heart beat whacking against my chestwall and hearing it in my ear. I therefore had a constant reminder of this irregularity, and frequently had the thought, "what if my heart stops" etc. Well it got to the point where I became very anxious about it, and started feeling breathless, and light headed. One night, it got really bad, and I thought I would keel over. Then this strange thought occured to me that if this breathlessness and dizziness was due to my heart, if I tried to run I wouldn't be able to. So I went on a 3 mile run, and realised that my heart must be fundamentally working if I could do that!! I did some relaxation techniques and it seemed to help. Now I'm not suggesting this course of action for you, but just that it is possible that the mind can be rather non-constructive when it wants to be. I'd agree that avoiding sugary caffeinated drinks is a good idea, and limit the tea and coffee. Try not to get too tired as well. These things, as well as alcohol, can really make you feel anxious. Eating alot of simple sugars can result in sugar highs and lows, and the lows can feel quite anxiety inducing - try to switch to more complex carbs. Don't suddenly diet either, as that can make you feel pretty weird! You can also try "diaphragmatic breathing" first and then "progressive muscular relaxation" which you may find helpful. Indeed, its pretty helpful thing to do anyway. As you said, follow up with the GP, and try to be reassured by the doctors you have seen. I hope that helps, but remember, that as informed as people are over the internet, if you can't speak to interactively, and examine / test a patient, you really can't give an accurate opinion as to what might be happening.