Without doing medical testing, it would be impossible to tell what was happening with your heart. However, from the description you gave, it sounds as though it could have been an episode of something called supraventricular tachycardia (SVT), in which the right atrium, or upper chamber, of your heart, spontaneously generates an inappropriately rapid electrical signal, stimulating the heart to beat in excess of 150 bpm. This may or may not be what was happening when you felt your heart beating rapidly. Regardless, you need to tell your parents or guardian and go get it checked out. Sometimes the types of symptoms you re describing are difficult to diagnose, because by the time the person is at the ER, frequently it has subsided. Nonetheless, depending on what, if anything, is actually wrong with you, these things can persist and get worse, with the episodes lasting longer until they cause the person other side effects such as chest pain, shortness of breath, low blood pressure, etc. Please tell your parents and go get it checked out, just to be on the safe side.