Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) potassium-aggravated myotonia ?
    ### Response:
    Potassium-aggravated myotonia is a disorder that affects muscles used for movement (skeletal muscles). Beginning in childhood or adolescence, people with this condition experience bouts of sustained muscle tensing (myotonia) that prevent muscles from relaxing normally.
    