Anxiety Disorders are:
• A group of related conditions, each with its own symptoms
• Similar, in that they share one thing in common: a persistent, excessive worry or fear in situations that are not threatening.

Signs and symptoms (adapted from National Alliance on Mental Illness)

Emotional symptoms:
• Feelings of apprehension or dread
• Feeling tense and jumpy
• Restlessness or irritability
• Anticipating the worst and being watchful for signs of danger

Physical symptoms:
• Pounding or racing heart and shortness of breath
• Upset stomach
• Sweating, tremors and twitches
• Headaches, fatigue and insomnia
• Upset stomach, frequent urination or diarrhea

Some types of Anxiety Disorders:

Obsessive-compulsive Disorder (OCD)
Obsessive-compulsive disorder  is characterized by repetitive, unwanted, intrusive thoughts (obsessions) and irrational, excessive urges to do certain actions (compulsions). Although people with OCD may know that their thoughts and behavior don’t make sense, they are often unable to stop them.

Panic Disorder
Sudden feelings of terror, or panic attacks, can strike without warning. They are often mistaken for a physical health problem due to the severity of symptoms, which includes chest pain, heart palpitations, dizziness, shortness of breath, and stomach upset.

Certain places, events, or objects can invoke strong, irrational fear. Most people with specific phobias have several triggers and will work hard to avoid their triggers. This fear and the attempt to control it can seem to take over a person’s life.

More information on Anxiety Disorders
National Alliance on Mental Illness, on Anxiety Disorders and Obsessive-compulsive Disorder

Internet Mental Health, on OCD and Panic Disorder, as well as other Anxiety Disorders
A detailed description of various disorders, including causation, prevalence, symptoms, course of the illness, treatment and outcome, plus reference material.