What is Anxiety?
According to the NIH, fear and anxiety are a part of life. You may feel anxious before you take a test or walk down a dark street. This kind of anxiety is useful - it can make you more alert or careful. It usually ends soon after you are out of the situation that caused it. But for millions of people in the United States, the anxiety doesn't go away, and gets worse over time. They may have chest pains or nightmares. They may even be afraid to leave home. These people have anxiety disorders. Types of anxiety disorders include:

• Pain disorder
• Obsessive-compulsive disorder (OCD)
  
  Obsessive-compulsive disorder is a human anxiety disorder characterized by involuntary intrusive thoughts. When a sufferer begins to acknowledge these intrusive thoughts, the sufferer then develops anxiety based on the dread that something bad will happen. The sufferer feels compelled to voluntarily perform irrational, time-consuming behaviors to diminish the anxiety.
  
  http://en.wikipedia.org/wiki/Obsessive%E2%80%93compulsive_disorder
  
  
• Post-traumatic stress disorder
  
  Post-Traumatic Stress Disorder, PTSD, is an anxiety disorder that can develop after exposure to a terrifying event or ordeal in which grave physical harm occurred or was threatened. Traumatic events that may trigger PTSD include violent personal assaults, natural or human-caused disasters, accidents, or military combat.
  
  People with PTSD have persistent frightening thoughts and memories of their ordeal and feel emotionally numb, especially with people they were once close to. They may experience sleep problems, feel detached or numb, or be easily startled.
  
  Anyone can get PTSD at any age. This includes war veterans and survivors of physical and sexual assault, abuse, accidents, disasters, and many other serious events.Not everyone with PTSD has been through a dangerous event. Some people get PTSD after a friend or family member experiences danger or is harmed. The sudden, unexpected death of a loved one can also cause PTSD.
  
  http://www.nimh.nih.gov/health/topics/post-traumatic-stress-disorder-ptsd/index.shtml
  
  
• Phobias
  
  A phobia is a persistent and irrational fear of a particular type of object, animal, activity, or situation. Specific phobias are a type of anxiety disorder in which exposure to the feared stimulus may provoke extreme anxiety or a panic attack. Specific phobias are among the most common form of anxiety affecting up to 10% of the population.
  
  Common phobias include the fear of particular animals (for instance, dogs or snakes), insects or spiders, high places, lightening, flying, and blood. People with specific phobias often realize their fear is irrational, but are unable to prevent it. Often a person avoids situations in which contact with the feared object or animal may occur -- for example, avoiding driving through tunnels, if tunnels are the subject of the specific phobia. This type of avoidance can interfere with job and social functioning.
  
  http://dictionary.reference.com/browse/phobia
  
  
• Generalized Anxiety Disorder (GAD)
  
  Generalized anxiety disorder is characterized by persistent, excessive, and unrealistic worry about everyday things. People with the disorder, which is also referred to as GAD, experience exaggerated worry and tension, often expecting the worst, even when there is no apparent reason for concern. They anticipate disaster and are overly concerned about money, health, family, work, or other issues. Sometimes just the thought of getting through the day produces anxiety. They don't know how to stop the worry cycle and feel it is beyond their control, even though they usually realize that their anxiety is more intense than the situation warrants.
  
  http://www.adaa.org/understanding-anxiety/generalized-anxiety-disorder-gad
  
  
• Anxiety Disorders and Chronic Pain
  
  Muscle tension, body soreness, headaches. For people with anxiety disorders, pain like this may be all too familiar. Pain can be a common symptom - and sometimes a good indicator - of an anxiety disorder, particularly generalized anxiety disorder (GAD). But beyond everyday aches and pains, some people will also suffer a diagnosed chronic pain disease such as arthritis or fibromyalgia. And a co-occurring chronic pain disease can make functioning even more difficult for someone with an anxiety disorder.
  
  http://www.adaa.org/understanding-anxiety/related-illnesses/other-related-conditions/chronic-pain
  

www.nimh.nih.gov
www.healthyminds.org