Roothie you gotta be cool with exercising when fasting. From the vids I've seen Zumba is a pretty vigurous workout. When you are fasting your metabolism is slowed and that also lowers your blood pressure. Add doing only half rations of lemonade where you are getting minimal carbs for energy and it's all adds up for a formula for trouble. Could possibly be that your system is working something out toxin related but because of the combo of factors above I would say it's more likely that your blood sugar got low and also the lower blood pressure and that is what made you ill.
In my MCs I also use half the syrup but on days when I've worked out I go full ration. The other time I got real wonky and nauseaus on the MC was on a job where I couldn't stop to even drink water so I blame that on dehydration. When I stopped and sipped down a qt of water I felt fine. Are you drinking water in addition to the lemonade?