Anxiety during social interactions, particularly between strangers, is common among young people. It may persist into adulthood and become social anxiety or social phobia. "Stranger anxiety" in small children is not considered a phobia. In adults, an excessive fear of other people is not a developmentally common stage; it is called social anxiety. According to Cutting, social phobics do not fear the crowd but the fact that they may be judged negatively.
Physical Symptoms: People with panic disorder may also have irritable bowel syndrome, characterized by intermittent bouts of gastrointestinal cramps and diarrhea or constipation, or a relatively minor heart problem called mitral valve prolapse, which can trigger panic attacks in some people. In fact, panic disorder often coexists with unexplained medical problems, such as chest pain not associated with a heart attack or chronic fatigue.
Neural circuitry involving the amygdala (which regulates emotions like anxiety and fear, stimulating the HPA Axis and sympathetic nervous system) and hippocampus (which is implicated in emotional memory along with the amygdala) is thought to underlie anxiety. People who have anxiety tend to show high activity in response to emotional stimuli in the amygdala. Some writers believe that excessive anxiety can lead to an overpotentiation of the limbic system (which includes the amygdala and nucleus accumbens), giving increased future anxiety, but this does not appear to have been proven.
Anxiety attacks, also called panic attacks, are episodes of intense fear and emotional distress that usually occur suddenly and without warning, and typically last from several minutes up to an hour. These attacks may have a discrete trigger, but they also can occur without any identifiable cause. Anxiety attacks are often recurrent, and are very distressing to the people who experience them, as well as their loved ones.
Biological causes may include obsessive compulsive disorder, Postural Orthostatic Tachycardia Syndrome, post traumatic stress disorder, hypoglycemia, hyperthyroidism, Wilson's disease, mitral valve prolapse, pheochromocytoma, and inner ear disturbances (labyrinthitis). Dysregulation of the norepinephrine system in the locus ceruleus, an area of the brain stem, has been linked to panic attacks.