I'm kind of out of shape, and I'm using the summer to get in better shape. I'm not heavy, I'm actually underweight (5"8' 107 lbs). Anyway, I was jumping rope pretty fast (2.5 turns a second or so) for about 10 minutes, when all of a sudden I felt an intense pulsing on the front of the left of my head, followed by an instant headache. I quit jump-roping and the headache went away a few minutes later. Is this a problem? Is there anything I can do to prevent it? *I'm not on any caffeine, I've recently eliminated it from my diet.