I get that sometimes, too. Actually, I just started doing the Guerilla Cardio this week, doing it as soon as I wake up and before I eat or anything. Completely empty stomach. And, honestly, I have to say that besides being worn out I feel great. No cramps or anything. Of course, maybe it's because the workout is so short, or maybe it's because it's done in a fairly fasted state. Anyway, just to let you know, I feel your pain, and when I do I usually just try to work through it.