Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Sleep Apnea ?
    ### Response:
    When you're awake, throat muscles help keep your airway stiff and open so air can flow into your lungs. When you sleep, these muscles relax, which narrows your throat.
                
Normally, this narrowing doesnt prevent air from flowing into and out of your lungs.
    