I am a 15 year old female, very healthy (I swim twice a week, am generally active all round, eat well and am of an average weight and height) but I often have heart palpitations, usually at least once every two days, have chest pains and this weird 'dropping' feeling in my heart region that takes the breath out of me after I run or exert myself in any way aside from swimming.

I get extremely light-headed from standing and almost every time I stand (even if I don't get up really fast) my vision goes black, my head hurts as if someone is pressing down hard on it, I feel very very faint and weak. These symptoms last roughly 15-30 seconds after I stand. Despite always almost fainting, I never actually HAVE but have been close to many a time.

I also have an extremely fast pulse (about 80bpm - 100bpm but shoots up to around 120+ when I stand and 140+ when I run for only a minute or so).

I can rule out anxiety as all of this happens even when I am completely calm. I am awaiting the results for an ECG but judging by the lack of urgent reply I imagine the results are regular but I was just wondering if anyone else may know what it is I am experiencing.