Dear Cathe and others: I have had something really strange happen to me 2x now. I am very fit and in-shape and am able to perform hour-long, intense exercises. However, on 2 different days (a few weeks apart), I had started to exercise one of my routines, and my body started tensing up and I felt like all the energy had been drained out of me. I literally thought I was going to fall over and had to stop exercising. Keep in mind I eat 3 healthy meals every day, I wasn't sick, I wasn't hot, and I had only been exercising for a few minutes when it happened. Also, I only exercise a few times a week. What in the world is this? It's scary.