response: The ultimate diagnosis is based on a person's symptoms.
history: My friend has chronic fatigue syndrome.  Its sad That's too bad. I'm aware that this limits a person's ability to do daily activities. Yes.  He has a lot of trouble doing even everyday things in life The cause isn't understood, but several different mechanisms have been proposed. Oh, really? How do they diagnose it, then?
knowledge: Diagnosis is based on a person's symptoms.