Jolt, one thing that I've started doing in spin class (or when I use the trainer at home) is put Nuun in my bottle. The added electrolytes seem to do the trick for me. Just make sure you get the Nuun R Natural, without the preservatives. I realized that I often feel as crappy as I do when I ride outside in very hot weather; it's all related to overheating. Find a bike by a fan or open window/door. I always wear a sleeveless jersey, too.