hi there, this incident took place today and i am really confused, i am 21 and work out everyday, today while i was taking a nap in the day my heart started pounding hard and slow, (slowing down) and i had a tingly rush through my whole body and i started shaking, more like vibrating, i was half awake but coudnt stop this no matter how hard i tried, it lasted for 20-30 seconds and was really scary, what could it be ? do i need to see a doctor ? Thanks