More on anxiety

Anxiety has emotional (an unpleasant feeling of dread or tension), cognitive (thinking related - fear of outcome of one's action or of negative evaluation by others), behavioral (avoidance of anxiety provoking situation), and physiological (heightened arousal, increased heart rate, blood pressure etc) components. But it is not a negative thing always.

It can have benefits in some situations. For example if you are doing tight rope walking or something similar which needs utmost attention and care; anxiety increase your attention and prevents mishaps. But if the anxiety is excess, the resultant increased arousal can lead to impaired performance. a child with very little anxiety about his exams may neglect studies. Too much anxiety can impair his ability to perform in the tests.
In conclusion, too much anxiety is bad; too little of is also damaging.
The major neurological structure responsible for anxiety is a small part of the brain called amygdala.
When anxiety becomes excessive and leads to significant distress or impairment in functioning of a person, it can be labelled as Anxiety disorders.
Currently the major anxiety disorders are
1) Panic disorder. Spontaneously occurring episodes of acute sever anxiety along with fast pounding hearts, tightness in chest, breathing difficulty, fear or losing control or mind going blank, intense fear etc. These episodes start mildly and increase in intensity over 19 to 15 minutes. many patients suffering from a panic attack are rushed to the emergency rooms and evaluated for heart diseases (angina, heart attack etc).
2) Phobic anxiety: Fear of animals, objects, height, darkness etc 9Simple phobia). In Social phobia there is fear of talking to others or performing in social situations. Such persons blush easily during social interactions. In all types of phobia affected persons tend to avoid such situations. They may also get panic attacks in such situations. Mere thoughts can also provoke panic attacks.
Other types of anxiety disorders are Obsessive compulsive disorder, Generalised anxiety disorder etc.
Anxiety disorders can also occur secondary to medical disorders (e g: thyroid disorders, Addison's disease, pheochromocytoma etc) and due to some medications. Hence it is advisable to rule out such conditions before making a diagnosis of anxiety disorders. Many people use alcohol to reduce anxiety and later become dependant on it.