You were not specific on the symptoms
you experience, but my guess is that when you exercise you don't drink water, or you sweat to excess. This will dehydrate you and you will lose salt and other minerals. You can experience shaking of the hands, visual disturbances, headaches, stomach aches, stitches in the sides, exhaustion, low grade temps and other unpleasant symptoms. If this is the case, try drinking a fluid that has minerals in it like Cytomax.