Anxiety is vital to our survival.  Unfortunately, excessive or unrealistic anxiety can be annoying at best and disabling at its worst.  Anxiety can paralyze us and change our behavior.  Fear is simply the emotion.  What we fear is the important factor.

"Fear is the main source of superstition, and one of the main sources of cruelty.  To conquer fear is the beginning of wisdom" -- Bertrand Russell

"Of all the liars in the world, sometimes the worst are your own fears." -- Rudyard Kipling

"Never let the fear of striking out get in your way." -- Babe Ruth

Types of Anxiety Disorders

Panic Attacks: 

Panic attacks are characterized by a rush of intense anxiety accompanied by several symptoms of anxiety such as shortness of breath, difficulty breathing, chest pains, dizziness, nausea, abdominal distress, feelings of unreality, fear of losing control, and fear of dying.

Some attacks may come "out of the blue" while others may be triggered by overwhelming circumstances.  Often people experiencing panic attacks will also experience fear of having another attack (anticipatory anxiety).  They may alter their behavior to avoid having another attack (usually by avoiding situations or thoughts that may trigger a panic attack)

Obsessive Compuslive Disorder: 

Obsessions are thoughts, images, or impulses that enter a person's mind involuntarily and are usually associated with increased distress or discomfort. 

Compulsions are behaivors (mental or physical) that the person does to try and decrease the distress or discomfort.  OCD is characterized by either obsessions or compulsions although most suffers experience both. 

Social Anxiety

Simple Phobias

Post-Traumatic Stress Disorder

Generalized Anxiety Disorder