Panic Disorder: This is sometimes referred to as an anxiety attack. It is characterized by intense anxiety, fear or discomfort that can be accompanied by a number of other features, including a rapid or pounding heartbeat, sweating, trembling or shaking, a feeling of not getting in a full breath or smothering sensation, feeling of choking, chest pain or discomfort, stomach upset, feeling dizzy or lightheaded, a detached or spacey feeling, fear of losing control or going crazy, fear of something medically horrible going on, numbness or tingling sensations (especially in the hands and arms and around the mouth), and chills or hot flushes. Some of these symptoms are caused by subtle or obvious hyperventilation. Attacks can have a clear trigger, or can come out of the blue. They can even awaken someone from sleep (so-called nocturnal panic). Sometimes people restrict their activities, or comfort zone of where they will go, which can lead to agoraphobia. With agoraphobia, people fear having panic attacks outside of their comfort zone.