Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Seasonal Affective Disorder ?
    ### Response:
    Some people experience a serious mood change during the winter months, when there is less natural sunlight. This condition is called seasonal affective disorder, or SAD. SAD is a type of depression. It usually lifts during spring and summer.     Not everyone with SAD has the same symptoms.
    