I'm not sure what you had throughout the day or what kind of exercise you're doing, but you might need to eat something that's a little more carb-heavy, especially if your exercise is high intensity activity. Here's an article about pre-workout eating that you might find helpful: www.sparkpeople.com/resource/nutrition_art
It's hard to know for sure, but it sounds like your blood sugar was a little low and that's why you started feeling this way. It's not a good idea to just try and push through it because that can make you feel even worse. One option is to stop, have a small snack with 20-30 grams of carbs in it and wait 10 minutes or so. If you feel better, then you can likely continue. Of course, if this becomes an ongoing issue you'll want to talk to your doctor about it.
Hope that helps,