The symptoms of a panic attack may cause the person to feel that their body is failing. The symptoms can be understood as follows. First, there is frequently the sudden onset of fear with little provoking stimulus. This leads to a release of adrenaline (epinephrine) which brings about the fight-or-flight response when the body prepares for strenuous physical activity. This leads to an increased heart rate (tachycardia), rapid breathing (hyperventilation) which may be perceived as shortness of breath (dyspnea), and sweating. Because strenuous activity rarely ensues, the hyperventilation leads to a drop in carbon dioxide levels in the lungs and then in the blood. This leads to shifts in blood pH (respiratory alkalosis or hypocapnia), causing compensatory metabolic acidosis activating chemosensing mechanisms which translate this pH shift into autonomic and respiratory responses. The person him/herself may overlook the hyperventilation, having become preoccupied with the associated somatic symptoms.
Anxiety disorders are characterized by a general feature of excessive fear (i.e. emotional response to perceived or real threat) and/or anxiety (i.e. worrying about a future threat) and can have negative behavioral and emotional consequences. Obsessive-compulsive and related disorders are characterized by obsessive, intrusive thoughts (e.g., constantly worrying about staying clean, or about one's body size) that trigger related, compulsive behaviors (e.g. repeated hand-washing, or excessive exercise). These behaviors are performed to alleviate the anxiety associated with the obsessive thoughts. Trauma- and stressor- related anxiety disorders are related to the experience of a trauma (e.g., unexpected death of a loved one, a car accident, or a violent incident) or stressor (e.g., divorce, beginning college, moving).
Occasional anxiety is an expected part of life. You might feel anxious when faced with a problem at work, before taking a test, or before making an important decision. But anxiety disorders involve more than temporary worry or fear. For a person with an anxiety disorder, the anxiety does not go away and can get worse over time. The symptoms can interfere with daily activities such as job performance, school work, and relationships.