Sometimes, younger people can have an irregular heart rhythm called SVT (supraventricular tachycardia) which is a rapid beating of your heart - often over 150 beats a minute. It can also spontaneously resolve on it s own which yours did. Trouble is, if this is what has occurred, it might be possible you could have another episode of this again. Since you state you are younger, these episodes can be months or even years apart. When you need to seek medical attention is if they do not stop on their own,or they are starting to become more and more frequent. Then, a Holter Monitor (a portable cardiac monitor that you wear for a period of time) might be able to capture what this rhythm actually is and then you could be treated with the appropriate medications to prevent it from recurring. It could also be other heart dysrhythmias but without someone hooking you up to a cardiac monitor WHILE it is occurring, there is no way to tell what the rhythm disturbance is that you are having. And, stress, extreme fatigue, street drugs and caffeine can also bring on these rhythm disturbances. These rhythms cause no damage to your heart but if they occur frequently, they need to be managed by medications.