Haha man, same thing happened to me. Even a week in I was struggling to run at basketball. Its not so bad now but its still noticeable. I was doing HIIT on the treadmil last week and it would not even take a heart rate reading. I assume its because it was so high. After walking for 5 mins it still read 160bpm and that was after i felt recovered.
So i dont take it before bball now! Its great at keeping away carb cravings though.