Hello and thank you for using HCM. I carefully read your question and I understand your concern, but don t worry, its nothing serious. A person might experience fast heart beats from different rhythm issues. It might be a sinus tachycardia, meaning that your heart beats over 100/beat for minute or another king of arrhythmia like supra-ventricular tachycardia.This gives you the sensation like your heart soddenly begins to run fast for few second and than it stops. It might give you difficulties in breathing deeply,cough and an anxiety sensation. In fact, all rhythm disturbances to the simplest one when the heart has its normal sinus rhythm to different arrhythmia when heart looses its normal rhythm can cause you this sensations that i explained above. They happen for different reasons from simple emotional stress to pathologyes like anemia, hyperthyroidism, ischemic heart disease ect. So, my opinion is that you should not worry. At your age this symptoms are most of times quite normal. Eventhogh you can do a simple chek up with a blood sample, your thyroid hormones, electrocardiogram, echo-cardiograph and a holter rhythm monitoring to see what are this sudden fast heart beats. Mean while avoid caffeine products because they exacerbate your symptoms. Hope I was helpful. Best regards.