Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) narcolepsy ?
    ### Response:
    Narcolepsy is a chronic sleep disorder that disrupts the normal sleep-wake cycle. Although this condition can appear at any age, it most often begins in adolescence.  Narcolepsy is characterized by excessive daytime sleepiness. Affected individuals feel tired during the day, and several times a day they may experience an overwhelming urge to sleep.
    