My 79 year old father has experienced dizziness, some cognitive problems, and extreme fatigue for the past three years. The onset of symptoms usually includes nasal congestion. When he is asymptomatic, he's fine mentally and physically, but he generally has a "bout" of whatever this is every month or so. He has seen every specialist imaginable, including a cardiologist, neurologist, ENT, endocrinologist, lung (can't recall the name for this!), gastroenterologist, psychologist, etc. He's had every scan and blood test imaginable, extensive testing for dementia, but every doctor is stumped. He is on medication for hypertension, a statin, and takes a very low dose of a steroid (don't know which one) for mild COPD. A reaction to medications has been tested and ruled out. We are so frustrated because, besides these troubling bouts of whatever it is, he's an active, engaged, and otherwise healthy guy for his age. His doctors have all but given up and many say the same thing: "you're an enigma." I know he's not a young man, but if he has something diagnosable and treatable, I'm sure he has a decade or more left. Any ideas would be appreciated...