I'm 17 years old, and quite athletic. Not obese or overweight, I weigh 170 lbs and am 5' 11" tall, 10% body fat, and a BMI (body mass index) of 23.

Anyway, I have had this minor problem for about 5 years now. My heart rate is very healthy, about 56 or so per minute. When I perform exercises especially running, (since I am a medium distance track and cross country runner as well as a weightlifter) my heart rate increases accordingly and is quite normal.

However, sometimes when I'm not doing anything exercise related, say walking or talking, if I take a sudden turn or say something suddenly, my heart rate increases rapidly, and beats really fast as if I was exercising at my maximum. It usually lasts only a minute or so, because I purposely start breathing deep and slowly, which makes my heart rate slow down to its normal rate.

This has happened about maybe once a month or so, and has had no repercussions to my health except for maybe feeling a bit lightheaded while it was beating abnormally fast.

It's happened a few times while I run to, which has caused me to stop running completely, sit down, and allow my heart rate to slow down to normal. And if it lasts a bit longer, I feel my heart thumping, and I can actually see my left chest muscle move in and out as the heart beats.

Can someone please tell me what this is, because I'll go to see a doctor if this is quite serious.

Thank you.

-Chris Fussman