Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Chronic Fatigue Syndrome ?
    ### Response:
    Chronic fatigue syndrome (CFS) is a disorder that causes extreme fatigue. This fatigue is not the kind of tired feeling that goes away after you rest. Instead, it lasts a long time and limits your ability to do ordinary daily activities.    The main symptom of CFS is severe fatigue that lasts for 6 months or more.
    