The best way to understand the nature of anxiety is to distinguish it from fear. For example, anxiety can be distinguished from fear in several ways. When you are afraid, your fear is usually directed toward a concrete, external object or situation. The event that you fear is within the bounds of possibility. You might fear missing a deadline, failing an exam, being unable to pay your bills, or being rejected by someone you want to please. When you experience anxiety, on the other hand, you often can't specify what it is you're anxious about. The focus of anxiety is more internal than external. It seems to be a response to a vague, distant, or even unrecognized danger. You might feel anxious about "losing control" of yourself, a situation, or a vague anxiety about "something bad happening or impending doom."

Anxiety affects your whole being. It is a physiological, behavioral, and psychological reaction all at once. On a physiological level, anxiety may include bodily reactions such as rapid heartbeat, muscle tension, nausea, dry mouth, or sweating. On a behavioral level, it can sabotage your ability to act, express yourself, or deal with certain everyday situations. Psychologically, anxiety is a subjective state of apprehension and uneasiness. In its most extreme form, it can cause you to feel detached from yourself and even fearful of dying or going crazy.

There are seven different types of anxiety disorders. Panic disorder is when the predominant feature is recurring panic attacks. This disorder can produce anticipatory anxiety (physical and emotional tension in anticipation of a panic attack). Panic disorder can also lead to agoraphobia, a marked fear or avoidance of being alone or of being in certain public places. The response is strong enough to significantly limit normal activities. Generalized anxiety disorder, a chronic state of tension which affects all systems in the body, is the third and most common type of anxiety disorder. Social phobia is an anxiety disorder that causes excessive or unreasonable fear that other people may notice and/or judge you. The persistent and irrational fear of an object or situation is categorized as a specific phobia. A severe type of anxiety disorder is termed obsessive-compulsive disorder. People who experience obsessive-compulsive disorder have obsessions (repetitive, unproductive thoughts) and compulsions (unproductive behaviors that are enacted ritualistically). A final type of anxiety disorder is posttraumatic stress disorder. This disorder identifies a specific emotional distress that follows a major psychologically traumatic event.