Below is an instruction from Human. Write a response.
    ### Instruction:
    How to diagnose Chronic Fatigue Syndrome (CFS) ?
    ### Response:
    Diagnostic Challenges
  
For doctors, diagnosing chronic fatigue syndrome (CFS) can be complicated by a number of factors:
  
   - There's no lab test or biomarker for CFS.
   - Fatigue and other symptoms of CFS are common to many illnesses.
   - For some CFS patients, it may not be obvious to doctors that they are ill.
    