Anxiety disorders are characterized by extreme fear, nervousness, or worry on exposure to a feared stimulus, which can be an object, person, or situation. Fear is differentiated from anxiety, in that fear is a reaction to a current stimulus, whereas anxiety is fear of some future stimulus or anticipation of one. Anxiety becomes a problem when you become fearful, nervous, or worried out of proportion to the feared stimulus, or become nervous or worried about some future stimulus or anticipated event.
Fear is a normal response, and is a necessary component of survival. When presented with danger in the environment, a physiological reaction is triggered where adrenaline is released into the bloodstream. Adrenaline is a fear-response hormone which causes several physical changes in the body, including increased heart rate, increased rate of breathing, and dilated pupils. In addition, there is shunting of the blood flow from the digestive system and the skin to the skeletal muscles, which can be felt as having the “butterflies” in the stomach or having numbness and tingling sensations of the extremities. These physical changes allow you to prepare to fight the danger, or to run from it, the so-called “fight-or-flight” response. The increased heart rate and breathing rate allows the blood to supply more oxygen to the skeletal muscles needed to fight or run, and the blood shunting to the skeletal muscles further aids this process. The dilated pupils allow for improved vision to assess the danger, and the brain becomes more alert and hypervigilant for danger, allowing you to scan your environment in order to deal with the external danger. However, this fear response goes awry when you start to anticipate danger, or start to have thoughts about events which overestimate the danger and underestimate your ability to cope with the danger. In this situation, the fear response is heightened by your thoughts about the event or future event, where the overestimation of danger and underestimating of your coping leads to anxiety. Unfortunately, the body perceives fear and anxiety the same way, where the adrenaline response is triggered with either fear or anxiety. So when you have anxiety, the fight-or-flight response is activated, and serves no purpose as the danger is more in your head and the way you think or give meaning to the situation.
Anxiety becomes an anxiety disorder when the anxiety symptoms cause impairment of functioning in relationships and work/school, and you have significant distress and are unable to control the anxiety. The major anxiety disorders include generalized anxiety disorder, specific phobia, social phobia, panic disorder, post traumatic stress disorder, and obsessive compulsive disorder.