You seem very young for any of this, but you might also be checked for sleep apnea. If you wake suddenly in the middle of the night and your heart is beating that fast, it's like you might have quit breathing and your heart is trying to get more oxygen by beating faster. I wore an oxygen meter all night last week to determine if I have sleep apnea. It was an easy test. I don't have the results yet but it wouldn't surprise me. Makes sense that your heart beats faster when it's deprived of oxygen.