Originally Posted by WarChild

So you don't experience the light headedness and dizziness until 40 minutes in to your work out?

You need more carbs pre-workout. The Banana is great simple carb, but mix it with a low glycemic value complex carb like oatmeal. Have a bowl of oatmeal with banana, or blueberries, before you work out. If you're really pushing yourself hard with max weights and THEN doing cardio afterwards, you can almost expect your blood to become glycogen depleted and that will cause the symptoms you're experiencing.

Listen to your body, it's telling you it's hungry. If you're doing heavy work outs you're going to need to supply heavy amounts of nutrients.