Fever, severe headache, and uncharacterisitc fatigue for four days is cause for concern of a serious infection of which meningitis is the most worrisome. Your son’s dysautinomia is also of concern especially if he has a sustained elevation in temperature which could strain his heart. With your son’s symptoms, his past medical history, and the fact that your son’s pediatrician is unavailable, it is highly recommended that you visit the emergency room to have your son evaluated.