Fear is an automatic neurophysiological state of alarm characterized by a fight or flight response to a cognitive appraisal of present or imminent danger (real or perceived). Anxiety is linked to fear and manifests as a future-oriented mood state that consists of a complex cognitive, affective, physiological, and behavioral response system associated with preparation for the anticipated events or circumstances perceived as threatening. Pathological anxiety is triggered when there is an overestimation of perceived threat or an erroneous danger appraisal of a situation which leads to excessive and inappropriate responses.
Anxiety disorders appear to be caused by an interaction of biopsychosocial factors. Genetic vulnerability interacts with situations that are stressful or traumatic to produce clinically significant syndromes.
Anxiety is one of the most common psychiatric disorders in the general population. Specific phobia is the most common with a 12-month prevalence rate of 12.1%. Social anxiety disorder is the next most common, with a 12-month prevalence rate of 7.4%. The least common anxiety disorder is agoraphobia with a 12-month prevalence rate of 2.5%. Anxiety disorders occur more frequently in females than in males with an approximate 2:1 ratio.
The significant mediators of anxiety in the central nervous system are thought to be norepinephrine, serotonin, dopamine, and gamma-aminobutyric acid (GABA). The autonomic nervous system, especially the sympathetic nervous system, mediates most of the symptoms.
The amygdala plays an important role in tempering fear and anxiety. Patients with anxiety disorders have been found to show heightened amygdala response to anxiety cues. The amygdala and limbic system structures are connected to prefrontal cortex regions, and prefrontal-limbic activation abnormalities may be reversed with psychological or pharmacologic interventions.
Characteristic Symptoms Pathological Anxiety
Cognitive symptoms: fear of losing control; fear of physical injury or death; fear of "going crazy"; fear of negative evaluation by others; frightening thoughts, mental images, or memories; perception of unreality or detachment; poor concentration, confusion, distractible; narrowing of attention, hypervigilance for threat; poor memory; and difficulty speaking.
Physiological symptoms: increased heart rate, palpitations; shortness of breath, rapid breathing; chest pain or pressure; choking sensation; dizzy, light-headed; sweaty, hot flashes, chills; nausea, upset stomach, diarrhea; trembling, shaking; tingling or numbness in arms and legs; weakness, unsteadiness, faintness; tense muscles, rigidity; and dry mouth.
Behavioral symptoms: avoidance of threat cues or situations; escape, flight; pursuit of safety, reassurance; restlessness, agitation, pacing; hyperventilation; freezing, motionless; and difficulty speaking.
Affective symptoms: nervous, tense, wound up; frightened, fearful, terrified; edgy, jumpy, jittery; and impatient, frustrated.
Anxiety Disorders as defined in the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM–5; American Psychiatric Association, 2013):
When the history and examination do not suggest the symptoms as arising from any other medical disorder, the initial laboratory studies may be limited to the following: complete blood cell count (CBC) chemistry profile, thyroid function tests, urinalysis, and urine drug screen.
If the anxiety symptoms are atypical or there are some abnormalities noted in the physical examination more detailed evaluations may be indicated to identify or exclude underlying medical conditions. This would include the following: electroencephalography, brain computed tomography (CT) scan, electrocardiography, tests for infection, arterial blood gas analysis, chest radiography, and thyroid function tests.
Treatment consists of psychotherapy, pharmacotherapy, or a combination of both.
Pharmacotherapy: selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), benzodiazepines, tricyclic antidepressants, mild tranquilizers, and beta-blockers treat anxiety disorders. 
Psychotherapy: One of the most effective forms of psychotherapy is cognitive-behavioral therapy. It is a structured, goal-oriented, and didactic form of therapy that focuses on helping individuals identify and modify characteristic maladaptive thinking patterns and beliefs that trigger and maintain symptoms. This form of therapy focuses on building behavioral skills so that patients can behave and react more adaptively to anxiety-producing situations. Exposure therapy is utilized to move individuals towards facing the anxiety-provoking situations and stimuli which they typically avoid. This exposure results in a reduction in anxiety symptoms as they learn that their anxiety is causing them to experience false alarms and they do not need to fear the situation or stimuli and can cope effectively with such a situation.
Characteristic features noted in individuals with clinical anxiety:
Anxiety disorders are very common and can present in diverse ways. When a person has chronic anxiety, the condition can be very debilitating and hence it is best managed by a multidisciplinary team consisting of a mental health nurse, psychiatrist, psychotherapist, social worker, and a primary care provider. The outlook for patients with anxiety is guarded. Data indicate that the high rates of mortality are associated with adverse cardiac events. In those with social phobia, the condition leads to significant functional impairment and a very poor quality of life. The risk of suicides is also high in this population. Patients with anxiety need lifelong follow up because, despite drug therapy, relapse rates are high. (Level V)