I do cardio on empty stomach and always get a pounding headache after. i drink h20. could empty stomach be cause? any damage i could be doing to self?

Could be!: You need calories to workout. Arnold Schwarzenegger in his book "Weight Training for Athletes," says he has acouple of oranges before he works out to get enough energy to get through the workout. Don't overeat, of course, but a small low fat snack like oranges (100 calories before a workout of 25-20 minutes) can give you the calories you need. Or try a couple of prunes or raisins.