From what I understand about rebounders is that when you start sneezing or feeling weak after doing that, it's actually good because your body is detoxing. So when you feel fatigued is because the rebounded is doing what it suppose to do. You immune is not getting weak, your getting stuff out of you. Although I use it myself I don't get those symptoms, I like using both machines. Walking in the nature is way better than any treadmill.