Why do MS sufferers suffer such exhaustion?

Its just one of our many symptoms. There is a drug for this symptom but I am not taking it yet. Some days are better than others. If you have M.S. talk with your Primary care Dr. or your Neurologist. Sometimes we have to do our own research then tell them what we need or want. And to think they are making a lot of money and we do all the work. Anyway this is what I have found.