Why do I get lightheaded and nauseous during working out?

Anonymous
Everytime I do a "harder" workout, like burpees (pushup-jump-squat) I get really lightheaded even though I only did like 5 burpees and I've eaten enough. When I do lighter workouts like running on a treadmill I feel like collapsing after 10mins?
By the way I am at a healthy weight and my BMI is 19.5.

Why do I get lightheaded and nauseous during working out?
7 Opinion