Sometimes my heart randomly starts beating really hard and fast. This happens even when I am sitting down and haven t been doing anything. It happened for the first time when I was 10 years old, (now 20) and it really scared me at first. It happens a few times a month and so now I am used to it. Sometimes it lasts a few minutes and sometimes it lasts for up to an hour. It causes me to be short of breath, and when it goes on for longer than usual I get that tired, worn out feeling that you get after you just ran a lap- even if I have been sitting still the whole time. Over these 10 years a few things I have noticed that make it more likely to happen (but don t always cause it to happen) are caffeine, stress, and anxiety. Another strange trigger that sets it off almost every time is if I bend down quickly to pick something up off the floor. I am not overweight, but I am very out of shape and so lately I have been playing frisbee and taking walks. I have been running only a little bit when I play frisbee. I haven t done any very intense exercise. I have only been doing this for 5 days now and every time I do I get this heart thing. And even when I m not exercising it s been happening. Today it happened 3 times. And I have only recorded my heart rate twice and I had it once at 160 bpm resting and then another at 184 bpm resting. Should I stop exercising before I hurt myself or should I keep exercising and try to help it? Although this doesn t hurt me when each instance occurs, is it hurting me long-term? What could this be?