What could cause dizziness, dry mouth, sore throat, muscle aching, and others during extreme exercise?

For a few months I have been plagued by awful symptoms during exercise. In volleyball when we would practice really hard, I would get nausea and feel weak and dizzy. As time went on it would get so bad I would have to leave practice, though I never actually threw up. Running the mile the past couple times causes awful pain in my ankles, shins and knees. I will get dizzy to the point where I can't run straight, and when I stop I can't stand for more than a minute. I may be out of shape, but none of my even more out of shape friends experience these symptoms.