Since graduating I have tried to continue doing a 30 min run at least once a week as well as doing some of the stepping stones run for speed. I have found recently that after about 25 min my left foot starts to tingle and by 30 min it goes almost completely numb, forcing me to stop. I then walk back home with it still numb. Once I sit down, everything comes back to normal within 5 -10 mins. Any suggestions as to why this is happening and what I can do about it?