Feeling anxious every now and then is a normal emotion. Many people feel nervous when faced with a problem at work, before taking a test, or making an important decision. Anxiety disorders are not the same. They cause distress that interferes with your ability to lead a normal life. This is excessive, unrealistic worry and tension when there is nothing to provoke the anxiety. This type of disorder is a serious mental illness. For people with this disorder, worry and fear are constant and overwhelming, and can be disabling.

Examples of anxiety disorders include panic attacks, obsessive-compulsive disorder, and post-traumatic stress disorder. People with panic disorder have feelings of terror that strike suddenly and repeatedly with no warning. Social anxiety disorder involves overwhelming worry and self-consciousness about everyday social situations. Specific phobias are intense fears of a specific object or situation, such as heights or flying. Treatment includes counseling or medications, including antidepressants.

The exact cause of anxiety disorders is unknown, but anxiety disorders -- like other forms of mental illness -- are not the result of personal weakness, a character flaw, or poor upbringing. As scientists continue their research on mental illness, it is becoming clear that many of these disorders are caused by a combination of factors, including changes in the brain and environmental stress.