Anxiety in small doses is healthy, but it can grow out of control, causing significant suffering and disability. A number of different disorders result from anxiety gone awry.

Generalized Anxiety Disoder (GAD) is exaggerated worry about everything or nothing that is present most of the time. People with GAD worry about health, finances, career, family, etc. -- even when there is no sign of trouble. GAD is out-of-control anxiety that is greater than the normal anxiety that everyone experiences. Its prevalence of about 2.8% in the U.S.

Obsessive-Compulsive Disorder (OCD) disables by stealing time from its victims. It starts with obsessions, or intrusive worries, which can only be mitigated by engaging in compulsions, or rituals that soothe the worries. An obsessive-compulsive person may, for instance, worry that the stove was left on and have to go check it -- over and over again. People suffering from OCD know that their obsessions and compulsions are irrational but are helpless to resist them. Common themes in OCD include a need to check on things, worries about contamination, a need for symmetry or neatness, and a need to count things.

Phobias are extreme, irrational fears that are grossly out of proportion to the thing that is feared. Many phobias involve things that were dangerous in our ancestors' world, such as spiders and snakes. A mentally healthy person may fear snakes, but a phobic person may literally be affected all day by just hearing a conversation about snakes. (Sorry if you are snake-phobic and reading this!) Social phobia, also called social anxiety, is a particularly disabling phobia. Social phobia is far more than shyness; those suffering from it feel they are being constantly watched and judged by others and are petrified of being embarrassed or humiliated, to the point that it interferes with their daily lives. Its prevalence is a whopping 3.7% in the U.S. (that's over 10 million people).

Panic disorder involves recurrent panic attacks that have no apparent cause. In a panic attack, a person may sweat, have a racing heart, have trouble breathing, and may feel out of control. Some people describe panic attacks as feeling like things are "crashing down" on them, or as if they are dying. In fact, a panic attack may be mistaken for a heart attack. Fear of having a panic attack in public may lead to a person becoming homebound, a condition called agoraphobia.

Post-traumatic stress disorder (PTSD) is an abnormal reaction to a life-threatening situation such as a physical or sexual assault, an accident, a disaster, or military combat. It is important to note that the trauma is completely subjective -- PTSD can be triggered by an event that does not appear serious to outsiders, as long as the person experiencing it felt intensely threatened. Symptoms include flashbacks (ranging from dreams to waking hallucinations), hypervigilance, dissociation (a feeling of disembodiment or unreality), sleep trouble, depression and anxiety, feelings of guilt, and irritability. Physical symptoms are common too, such as headaches, digestive problems, chest pain, and immune system problems. Substance abuse is very common in those with untreated PTSD.

Sources and more information

• GAD, OCD, social anxiety, panic disorder, and PTSD (Freedom From Fear)