Anxiety disorders are often debilitating chronic conditions, which can be present from an early age or begin suddenly after a triggering event. They are prone to flare up at times of high stress and are frequently accompanied by physiological symptoms such as headache, sweating, muscle spasms, palpitations, and hypertension, which in some cases lead to fatigue or even exhaustion.

Although in casual discourse the words anxiety and fear are often used interchangeably, in clinical usage, they have distinct meanings; anxiety is defined as an unpleasant emotional state for which the cause is either not readily identified or perceived to be uncontrollable or unavoidable, whereas fear is an emotional and physiological response to a recognized external threat. The term anxiety disorder, however, includes fears as well as anxieties. Indeed, phobias (fears which are "persistent or irrational") constitute the majority of anxiety disorder cases.

Anxiety disorders are often comorbid with other mental disorders, particularly clinical depression. Studies have also indicated that anxiety disorders are more likely among those with family history of anxiety disorders, especially certain types.

Clinical and animal studies suggest a correlation between anxiety disorders and difficulty in maintaining balance. A possible mechanism is malfunction in the parabrachial nucleus, a structure in the brain, that among other functions, coordinates signals from the amygdala with input concerning balance. The amygdala is involved in the emotion of fear.

Especially the basolateral amygdala has been implicated in anxiety generation. A relationship between anxiety and dendritic arborization of the amygdaloid neurons is well known. SK2 potassium channels mediate inhibitory influence on action potentials and reduces arborization. By overexpressing SK2 in basolateral amygdala anxiety was reduced and stress-induced corticosterone secretion at a systemic level lowered, in a test model.

Mutations in related SK3 are suspected to be a possible underlying cause for several neurological disorders, including anxiety.

Biochemical factors come into play. Low levels of GABA, a neurotransmitter that reduces overactivity in the central nervous system, contributes to anxiety. A number of anxiolytics achieve their effect by modulating the GABA receptors.

Selective serotonin reuptake inhibitors, the drugs most commonly used to treat depression, are also frequently considered as a first line treatment for anxiety disorders. A recent study using functional brain imaging techniques suggests that the effects of SSRIs in alleviating anxiety may result from a direct action on GABA neurons rather than as a secondary consequence of mood improvement.

Approximately half of patients attending mental health services for conditions including anxiety disorders such as panic disorder or social phobia are the result of alcohol or benzodiazepine dependence. Sometimes anxiety pre-existed alcohol or benzodiazepine dependence but the alcohol or benzodiazepine dependence act to keep the anxiety disorders going and often progressively making them worse. Many people who are addicted to alcohol or prescribed benzodiazepines when it is explained to them they have a choice between ongoing ill mental health or quitting and recovering from their symptoms decide on quitting alcohol and/or their benzodiazepines. It was noted that every individual has an individual sensitivity level to alcohol or sedative hypnotic drugs and what one person can tolerate without ill health another will suffer very ill health and that even moderate drinking can cause rebound anxiety syndromes and sleep disorders. A person who is suffering the toxic effects of alcohol or benzodiazepines will not benefit from other therapies or medications as they do not address the root cause of the symptoms which is a "poisoned brain". Recovery from benzodiazepines tends to take a lot longer than recovery from alcohol but people can regain their previous good health. Symptoms may temporarily worsen however, during alcohol withdrawal or benzodiazepine withdrawal.

Intoxication from stimulants is likely to be associated with repetitive panic attacks.

There is evidence that chronic exposure to organic solvents in the work environment can be associated with anxiety disorders. Painting, varnishing and carpetlaying are some of the jobs in which significant exposure to organic solvents may occur.

Generalized anxiety disorder

Generalized anxiety disorder is a common chronic disorder characterized by long-lasting anxiety that is not focused on any one object or situation. Those suffering from generalized anxiety experience non-specific persistent fear and worry and become overly concerned with everyday matters.

Panic disorder

In panic disorder, a person suffers from brief attacks of intense terror and apprehension, often marked by trembling, shaking, confusion, dizziness, nausea, difficulty breathing. These panic attacks, defined by the APA as fear or discomfort that abruptly arises and peaks in less than ten minutes, can last for several hours and can be triggered by stress, fear, or even exercise; although the specific cause is not always apparent.

In addition to recurrent unexpected panic attacks, a diagnosis of panic disorder also requires that said attacks have chronic consequences: either worry over the attacks' potential implications, persistent fear of future attacks, or significant changes in behavior related to the attacks. Accordingly, those suffering from panic disorder experience symptoms even outside of specific panic episodes. Often, normal changes in heartbeat are noticed by a panic sufferer, leading them to think something is wrong with their heart or they are about to have another panic attack. In some cases, a heightened awareness (hypervigilance) of body functioning occurs during panic attacks, wherein any perceived physiological change is interpreted as a possible life threatening illness (i.e. extreme hypochondriasis).

Phobias

The single largest category of anxiety disorders is that of Phobia, which includes all cases in which fear and anxiety is triggered by a specific stimulus or situation. Sufferers typically anticipate terrifying consequences from encountering the object of their fear, which can be anything from an animal to a location to a bodily fluid.

Agoraphobia

Agoraphobia is the specific anxiety about being in a place or situation where escape is difficult or embarrassing. Agoraphobia is strongly linked with panic disorder and is often precipitated by the fear of having a panic attack. A common manifestation involves needing to be in constant view of a door or other escape route. In addition to the fears themselves, the term agoraphobia is often used to refer to avoidance behaviors that sufferers often develop. For example, following a panic attack while driving, someone suffering from agoraphobia may develop anxiety over driving and will therefore avoid driving in the future. These avoidance behaviors can often have serious consequences; in severe cases, one can even be confined to one's home.

Social anxiety disorder

Social anxiety disorder (also known as social phobia) describes an intense fear of negative public scrutiny or of public embarrassment or humiliation. This fear can be specific to particular social situations (such as public speaking) or, more typically, is experienced in most (or all) social interactions. Social anxiety often manfiests specific physical symptoms, including blushing, sweating, and difficulty speaking. Like with all phobic disorders, those suffering from social anxiety will attempt to avoid the source of their anxiety; in the case of social anxiety this is particularly problematic, and in severe cases can lead to complete social isolation.

Obsessive-compulsive disorder

Obsessive compulsive disorder is a type of anxiety disorder primarily characterized by repetitive obsessions (distressing, persistent, and intrusive thoughts or images) and compulsions (urges to perform specific acts or rituals). The OCD thought pattern may be likened to superstitions insofar as it involves a belief in a causative relationship where, in reality, one does not exist. Often the process is entirely illogical; for example, the compulsion of walking in a certain pattern may be employed to alleviate the obsession of impending harm. And in many cases, the compulsion is entirely inexplicable, simply an urge to complete a ritual triggered by nervousness.

In a minority of cases, sufferers of OCD may only experience obsessions, with no overt compulsions; a much smaller number of sufferers experience only compulsions.

Post-traumatic stress disorder

Post-traumatic stress disorder or PTSD is an anxiety disorder which results from a traumatic experience. Post-traumatic stress can result from an extreme situation, such as combat, rape, hostage situations, or even serious accident. It can also result from long term (chronic) exposure to a severe stressor, for example soldiers who endure individual battles but cannot cope with continuous combat. Common symptoms include flashbacks, avoidant behaviors, and depression.

Separation anxiety

Separation anxiety disorder is the feeling of excessive and inappropriate levels of anxiety over being separated from a person or place. Separation anxiety itself is a normal part of development in babies or children, and it is only when this feeling is excessive or inappropriate that it can be considered a disorder. Separation anxiety disorder affects roughly 7% of adults and 4% of children, but the childhood cases tend to be more severe, in some instances even a brief separation can produce panic.

Treatment options available include lifestyle changes; psychotherapy, especially cognitive behavioral therapy; and pharmaceutical therapy. Education, reassurance and some form of cognitive-behavioral therapy should almost always be used in treatment, while medications should not always be used.

Medications commonly prescribed for anxiety disorders include benzodiazepines, such as alprazolam (Xanax) and diazepam (Valium); antidepressants, including SSRI such as paroxetine (Paxil) and venlafaxine (Effexor), GABA analogues such as gabapentin or pregabalin, TCAs such as imipramine, and MAOIs; as well as atypical antipsychotics such as quetiapine, and piperazines such as hydroxyzine.

Treatment controversy arises because while some studies indicate that a combination of medication and psychotherapy can be more effective than either one alone; others suggest pharmacological interventions are largely palliative, and can actually interfere with the mechanisms of successful therapy. Meta-analysis indicates that psychotherapeutic interventions have superior long-term efficacy when compared to pharmacotherapy. However, the right treatment may very much depend on the individual patient's genetics and environmental factors.

Reducing caffeine, regular aerobic exercise and improving sleep hygiene are often useful in treating anxiety.