havn t been doing any physical activity for over a year and i ve just gotten back into running. i started with high intensity interval training (run for 30 seconds as hard as possible, then walk for a minute) right away did it for 2 nights like this: 5 min jog 4 mins of HIIT then id mix between walking and running. on the third night i did 5mins jog then 6 mins of HIIT and at the end of the HIIT i experienced pains in my heart area and had a really high heart rate also it felt weird when i took a deep breath but not a normal breath, i started walking and the pain went away, then when i started to jog again the pain came back after a while when my heart rate increased. i dont have a history of anything like this before and neither do any of my family. Am i just starting out too high for this sort of stuff and take it down a noch? btw im 17, 5 11 , and 181lbs.