Okay, this has been happening for a couple years now. My heart will spontaneously begin beating fast. It happens mostly when I bend over, like doing chores. I've told my family and we've begun to notice it happens once or twice a month. The quickened beating last about 2-3 minutes after it begins and spikes to about 160 or so. My normal heart rate is around 90-100 I believe. I am only a 14 year old girl. I weigh around 155-160 and I'm 6'0". I exercise about 3 times a week, swimming for about 1 hr. 15 min. on a team. After the 'attack', I normally feel dizzy or faint, I see black, and I feel breathless. The black goes away in seconds, but I feel dizzy and out of breath for a max. of 10 minutes. I normally lie down or sit when it starts, and you can see my chest moving. If you know what this is please help, it'll be much easier for me to deal with this when I know what it is.