What Could Cause A Random Pounding Heart ?

what could cause a random pounding heart in a 17 year old? for the last couple of months i ve experienced probably 5-6 times a really fast, pounding heart when I haven t done anything. it feels like i ve just ran a marathon when i ve just been sitting. 3-4 of the times it s been when im just laying in bed trying to fall asleep. It seems strange to me especially becuase i m so young. I ve heard it s possible to be connected with anxiety, which I do struggle with. it doesn t last very long at all, maybe a minute and a half max. I am also short of breath when it happens. I ve also seemed to get worked up easier while running or doing activities, but i ve only noticed this happenign since i gave blood. a couple hrs after i had given blood i half-ran up the stairs [like i always do, i almost never walk up steps for some reason] and i was insanely out of breath when i got to the top. which i assumed had something to dow ith having given blood. and it s seemed to get a little better since then, but i ve never gotten back to normal where i can just run up the stairs without being out of breath at all. I don t smoke or anything like that. anyway. what I mostly wanted to know is if this could just be nothing or if I need to go to the dr or something ?