So I've taken about 3 weeks off training to clear up all my injuries. I went for a jog today and decided to head on up to the park for some sprints. Let me say that I havn't ran a sprint in years so this was very hard for me. I ran 100M then jogged back about 5 times. After this...I felt messed up. I almost puked and my lungs felt very tight and it was the hardest time I've had breathing in a while. Was this too much too soon? Or is this part of the HIIT experience?