Hi i just started working out again recently and its not too intense i do interval training on a treadmill where i walk for 2 mins and run for 1 minute and i do this for 20 mins but i've been noticing that every-time i finish working out my heartbeat goes so fast that i can hear it in my head and sitting down doesnt seem to help and its hard for me to focus on anything with my eyes and i get a huge headache too and breath heavily but after ten mins i feel fine and all of this is gone i decided to write to you because today's episode was the worst i've had so far and it really freaked me out so please help me out and let me know what you think it could be. I am 21 years old 5'6 and my weight is 147lbs