Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Anxiety Disorders ?
    ### Response:
    In panic disorder, a person has sudden, unexplained attacks of terror, and often feels his or her heart pounding. During a panic attack, a person feels a sense of unreality, a fear of impending doom, or a fear of losing control. Panic attacks can occur at any time.
    