Distinguishing a Lengthly Mononucleosis Convalescence from a CFS diagnosis

[Donny]

How exactly does the medical community distinguish a lengthy recovery from Infectious Mononucleosis from a diagnosis of Chronic Fatigue Syndrome?

As reported in current research some people experience a pro-longed "post viral fatigue" after IM. Cases have been reported where patients experience a type of "post viral fatigue" that can last well past 6 months.

My question is how exactly do medical practitioners distinguish between on the diagnosis of these 2 separate conditions considering the over-lapping symptoms?

What are the implications that Doctors make a CFS diagnosis, a completely separate condition from IM, when in fact IM has already been documented at the onset?