The American Psychiatric Association introduced GAD as a diagnosis in the DSM-III in 1980, when anxiety neurosis was split into GAD and panic disorder. The definition in the DSM-III required uncontrollable and diffuse anxiety or worry that is excessive and unrealistic and persists for 1 month or longer. High rates in comorbidity of GAD and major depression led many commentators to suggest that GAD would be better conceptualized as an aspect of major depression instead of an independent disorder. Many critics stated that the diagnostic features of this disorder were not well established until the DSM-III-R. Since comorbidity of GAD and other disorders decreased with time, the DSM-III-R changed the time requirement for a GAD diagnosis to 6 months or longer. The DSM-IV changed the definition of "excessive worry" and the number of associated psychophysiological symptoms required for a diagnosis. Another aspect of the diagnosis the DSM-IV clarified was what constitutes a symptom as occurring "often". The DSM-IV also required difficulty controlling the worry to be diagnosed with GAD. The DSM-5 emphasized that excessive worrying had to occur more days than not and on a number of different topics. It has been stated that the constant changes in the diagnostic features of the disorder have made assessing epidemiological statistics such as prevalence and incidence difficult, as well as increasing the difficulty for researchers in identifying the biological and psychological underpinnings of the disorder. Consequently, making specialized medications for the disorder is more difficult as well. This has led to the continuation of GAD being medicated heavily with SSRIs.

The diagnosis of an anxiety disorder requires first ruling out an underlying medical cause. Diseases that may present similar to an anxiety disorder, including certain endocrine diseases (hypo- and hyperthyroidism, hyperprolactinemia), metabolic disorders (diabetes), deficiency states (low levels of vitamin D, B2, B12, folic acid), gastrointestinal diseases (celiac disease, non-celiac gluten sensitivity, inflammatory bowel disease), heart diseases, blood diseases (anemia), and brain degenerative diseases (Parkinson's disease, dementia, multiple sclerosis, Huntington's disease).

Also, several drugs can cause or worsen anxiety, whether in intoxication, withdrawal, or from chronic use. These include alcohol, tobacco, cannabis, sedatives (including prescription benzodiazepines), opioids (including prescription pain killers and illicit drugs like heroin), stimulants (such as caffeine, cocaine and amphetamines), hallucinogens, and inhalants.

As noted by Altman, McGoey & Sommer, it is important to observe the child, "in multiple contexts, on numerous occasions, and in their everyday environments (home, daycare, preschool)". It is beneficial to view parent and child interactions and behaviors that may contribute to SAD.

Dyadic Parent-Child Interaction Coding System and recently the Dyadic Parent-Child Interaction Coding System II (DPICS II) are methods used when observing parents and children interactions.

Separation Anxiety Daily Diaries (SADD) have also been used to “assess anxious behaviors along with their antecedents and consequences and may be particularly suited to SAD given its specific focus on parent–child separation” (Silverman & Ollendick, 2005). The diaries are carefully evaluated for validity.

This form of assessment should not be the sole basis of a SAD diagnosis. It is also important to verify that the child who is reporting on their experiences has the cognitive and communication skills appropriate to accurately comprehend and respond to these measurements.

An example of a self-report tool that has been tested is: The Separation Anxiety Assessment Scale for Children (SAAS-C). The scale contains 34 items and is divided into six dimensions. The dimensions in order are: Abandonment, Fear of Being Alone, Fear of Physical Illness, Worry about Calamitous Events, Frequency of Calamitous Events, and Safety Signal Index. The first five dimensions have a total of five items while the last one contains nine items. The scale goes beyond assessing symptoms; it focuses on individual cases and treatment planning.

The diagnostic criteria for GAD as defined by the Diagnostic and Statistical Manual of Mental Disorders DSM-5 (2013), published by the American Psychiatric Association, are paraphrased as follows:

No major changes to GAD have occurred since publication of the Diagnostic and Statistical Manual of Mental Disorders (2004); minor changes include wording of diagnostic criteria.

Anxiety disorders are often severe 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, tachycardia, palpitations, and hypertension, which in some cases lead to fatigue.

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" includes fears (phobias) as well as anxieties.

The diagnosis of anxiety disorders is difficult because there are no objective biomarkers, it is based on symptoms, which typically need to be present at least six months, be more than would be expected for the situation, and decrease functioning. Several generic anxiety questionnaires can be used to detect anxiety symptoms, such as the State-Trait Anxiety Inventory (STAI), the Generalized Anxiety Disorder 7 (GAD-7), the Beck Anxiety Inventory (BAI), the Zung Self-Rating Anxiety Scale, and the Taylor Manifest Anxiety Scale. Other questionnaires combine anxiety and depression measurement, such as the Hamilton Anxiety Rating Scale, the Hospital Anxiety and Depression Scale (HADS), the Patient Health Questionnaire (PHQ), and the Patient-Reported Outcomes Measurement Information System (PROMIS). Examples of specific anxiety questionnaires include the Liebowitz Social Anxiety Scale (LSAS), the Social Interaction Anxiety Scale (SIAS), the Social Phobia Inventory (SPIN), the Social Phobia Scale (SPS), and the Social Anxiety Questionnaire (SAQ-A30).

Anxiety disorders often occur along with other mental disorders, in particular depression, which may occur in as many as 60% of people with anxiety disorders. The fact that there is considerable overlap between symptoms of anxiety and depression, and that the same environmental triggers can provoke symptoms in either condition, may help to explain this high rate of comorbidity.

Studies have also indicated that anxiety disorders are more likely among those with family history of anxiety disorders, especially certain types.

Sexual dysfunction often accompanies anxiety disorders, although it is difficult to determine whether anxiety causes the sexual dysfunction or whether they arise from a common cause. The most common manifestations in individuals with anxiety disorder are avoidance of intercourse, premature ejaculation or erectile dysfunction among men and pain during intercourse among women. Sexual dysfunction is particularly common among people affected by panic disorder (who may fear that a panic attack will occur during sexual arousal) and posttraumatic stress disorder.

The DSM-IV-TR diagnostic criteria for panic disorder require unexpected, recurrent panic attacks, followed in at least one instance by at least a month of a significant and related behavior change, a persistent concern of more attacks, or a worry about the attack's consequences. There are two types, one with and one without agoraphobia. Diagnosis is excluded by attacks due to a drug or medical condition, or by panic attacks that are better accounted for by other mental disorders.

The diagnostic criteria:

The essential feature is recurrent attacks of severe anxiety (panic), which are not restricted to any particular situation or set of circumstances and are therefore unpredictable.

The dominant symptoms include:

- sudden onset of palpitations

- chest pain

- choking sensations

- dizziness

- feelings of unreality (depersonalization or derealization)

- secondary fear of dying, losing control, or going mad

Panic disorder should not be given as the main diagnosis if the person has a depressive disorder at the time the attacks start; in these circumstances, the panic attacks are probably secondary to depression.

The Panic Disorder Severity Scale (PDSS) is a questionnaire for measuring the severity of panic disorder.

Panic disorder typically begins during early adulthood; roughly half of all people who have panic disorder develop the condition before age 24, especially those subjected to traumatic experiences. However, some sources say that the majority of young people affected for the first time are between the ages of 25 and 30. Women are twice as likely as men to develop panic disorder and it occurs more often in people with above average intelligence.

Panic disorder can continue for months or years, depending on how and when treatment is sought. If left untreated, it may worsen to the point where one's life is seriously affected by panic attacks and by attempts to avoid or conceal the condition. In fact, many people have had problems with personal relationships or employment while struggling to cope with panic disorder. Some people with panic disorder may conceal their condition because of the stigma of mental illness. In some individuals, symptoms may occur frequently for a period of months or years, then many years may pass without symptoms. In some cases, the symptoms persist at the same level indefinitely. There is also some evidence that many individuals (especially those who develop symptoms at an early age) may experience symptom cessation later in life (e.g. past age 50).

In 2000, the World Health Organization found prevalence and incidence rates for panic disorder to be very similar across the globe. Age-standardized prevalence per 100,000 ranged from 309 in Africa to 330 in East Asia for men and from 613 in Africa to 649 in North America, Oceania, and Europe for women.

ICD-10 defines social phobia as a fear of scrutiny by other people leading to avoidance of social situations. The anxiety symptoms may present as a complaint of blushing, hand tremor, nausea or urgency of micturition. Symptoms may progress to panic attacks.

Standardized rating scales such as the Social Phobia Inventory, the SPAI-B, Liebowitz Social Anxiety Scale, and the Social Interaction Anxiety Scale can be used to screen for social anxiety disorder and measure the severity of anxiety.

Prevention of anxiety disorders is one focus of research. Use of CBT and related techniques may decrease the number of children with social anxiety disorder following completion of prevention programs.

In the opinion of Allen Frances, chair of the DSM-IV task force, the DSM-5's somatic symptom disorder brings with it a risk of mislabeling a sizable proportion of the population as mentally ill. “Millions of people could be mislabeled, with the burden falling disproportionately on women, because they are more likely to be casually dismissed as ‘catastrophizers’ when presenting with physical symptoms.”

Somatic symptom disorder has been a controversial diagnosis, since it was historically based primarily on negative criteria - that is, the absence of a medical explanation for the presenting physical complaints. Consequently, any person suffering from a poorly understood illness can potentially fulfill the criteria for this psychiatric diagnosis, even if they exhibit no psychiatric symptoms in the conventional sense. In 2013-4, there were several widely publicized cases of individuals being involuntarily admitted to psychiatric wards on the basis of this diagnosis alone. This has raised concerns about the consequences of potential misuse of this diagnostic category.

The ICD-10 defines hypochondriasis as follows:

The DSM-IV defines hypochondriasis according to the following criteria:

A. Preoccupation with fears of having, or the idea that one has, a serious disease based on the person's misinterpretation of bodily symptoms.

B. The preoccupation persists despite appropriate medical evaluation and reassurance.

C. The belief in Criterion A is not of delusional intensity (as in Delusional Disorder, Somatic Type) and is not restricted to a circumscribed concern about appearance (as in Body Dysmorphic Disorder).

D. The preoccupation causes clinically significant distress or impairment in

social, occupational, or other important areas of functioning.

E. The duration of the disturbance is at least 6 months.

F. The preoccupation is not better accounted for by Generalized Anxiety Disorder, Obsessive-Compulsive Disorder, Panic Disorder, a Major Depressive Episode, Separation Anxiety, or another Somatoform Disorder.

The newly published DSM-5 replaces the diagnosis of hypochondriasis with "illness anxiety disorder".

The basis of the diagnosis is the presence of a precipitating stressor and a clinical evaluation of the possibility of symptom resolution on removal of the stressor due to the limitations in the criteria for diagnosing AD. In addition, the diagnosis of AD is less clear when patients are exposed to stressors long-term, because this type of exposure is associated with AD and major depressive disorder (MDD) and generalized anxiety disorder (GAD).

Some signs and criteria used to establish a diagnosis are important. First, the symptoms must clearly follow a stressor. The symptoms should be more severe than would be expected. There should not appear to be other underlying disorders. The symptoms that are present are not part of a normal grieving for the death of family member or other loved one.

Adjustment disorders have the ability to be self-limiting. Within five years of when they are originally diagnosed, approximately 20%–50% of the sufferers go on to be diagnosed with psychiatric disorders that are more serious.

Most people who present to mental health specialists develop agoraphobia after the onset of panic disorder. Agoraphobia is best understood as an adverse behavioral outcome of repeated panic attacks and subsequent anxiety and preoccupation with these attacks that leads to an avoidance of situations where a panic attack could occur. Early treatment of panic disorder can often prevent agoraphobia. Agoraphobia is typically determined when symptoms are worse than panic disorder, but also do not meet the criteria for other anxiety disorders such as depression. In rare cases where agoraphobics do not meet the criteria used to diagnose panic disorder, the formal diagnosis of agoraphobia without history of panic disorder is used (primary agoraphobia).

DSM-5 diagnostic criteria for a panic attack include a discrete period of intense fear or discomfort, in which four (or more) of the following symptoms developed abruptly and reached a peak within minutes:

- Palpitations, and/or accelerated heart rate

- Sweating

- Trembling or shaking

- Sensations of shortness of breath or being smothered

- Feeling of choking

- Chest pain or discomfort

- Nausea or abdominal distress

- Feeling dizzy, unsteady, lightheaded, or faint

- Derealization (feelings of unreality) or depersonalization (being detached from oneself)

- Fear of losing control or going insane

- Sense of impending death

- Paresthesias (numbness or tingling sensations)

- Chills or hot flashes

In DSM-5, culture-specific symptoms (e.g., tinnitus, neck soreness, headache, and uncontrollable screaming or crying) may be seen. Such symptoms should not count as one of the four required symptoms.

Some or all of these symptoms can be found in the presence of a pheochromocytoma.

Screening tools such as the Panic Disorder Severity Scale can be used to detect possible cases of disorder and suggest the need for a formal diagnostic assessment.

Most research indicates that cognitive behavioral therapy (CBT) is an effective treatment for hypochondriasis. Much of this research is limited by methodological issues. A small amount of evidence suggests that selective serotonin reuptake inhibitors can also reduce symptoms, but further research is needed.

International Statistical Classification of Diseases and Related Health Problems, mostly known as "ICD", assigns codes to classify diseases, symptoms, complaints, social behaviors, injuries, and such medical-related findings.

ICD 10 classifies adjustment disorders under F40-F48 and under neurotic, stress-related and somatoform disorders.

According to the fourth revision of the "Diagnostic and Statistical Manual of Mental Disorders", phobias can be classified under the following general categories:

- Animal type – Fear of dogs, cats, rats and/or mice, pigs, cows, birds, spiders, or snakes.

- Natural environment type – Fear of water (aquaphobia), heights (acrophobia), lightning and thunderstorms (astraphobia), or aging (gerascophobia).

- Situational type – Fear of small confined spaces (claustrophobia), or the dark (nyctophobia).

- Blood/injection/injury type – this includes fear of medical procedures, including needles and injections (trypanophobia), fear of blood (hemophobia) and fear of getting injured.

- Other – children's fears of loud sounds or costumed characters.

Main features of diagnostic criteria for specific phobia in the DSM-IV-TR:

- Marked and persistent fear that is excessive or unreasonable, cued by the presence or anticipation of a specific object or situation (e.g., flying, heights, animals, receiving an injection, seeing blood).

- Exposure to the phobic stimulus almost invariably provokes an immediate anxiety response, which may take the form of a situationally bound or situationally predisposed panic attack. In children, the anxiety may be expressed by crying, tantrums, freezing, or clinging.

- The person recognizes that the fear is excessive or unreasonable. In children, this feature may be absent.

- The phobic situation(s) is avoided or else is endured with intense anxiety or distress.

Specific Phobia – DSM 5 Criteria

- Fear or anxiety about a specific object or situation (In children fear/anxiety can be expressed by crying, tantrums, freezing, or clinging)

- The phobic object or situation almost always provokes immediate fear or anxiety

- The phobic object or situation is avoided or endured with intense fear or anxiety

- The fear or anxiety is out of proportion to the actual danger posed by the specific object or situation and to the sociocultural context

- The fear, anxiety, or avoidance is persistent, typically lasting for 6 months or more

- The fear, anxiety, or avoidance causes clinically significant distress or impairment in social, occupational, or other important areas of functioning

- The disturbance is not better explained by symptoms of another mental disorder, including fear, anxiety, and avoidance of situations associated with panic-like symptoms or other incapacitating symptoms; objects or situations related to obsessions; reminders of traumatic events; separation from home or attachment figures; or social situations

Panic disorder can be effectively treated with a variety of interventions, including psychological therapies and medication with the strongest and most consistent evidence indicating that cognitive behavioral therapy has the most complete and longest duration of effect, followed by specific selective serotonin reuptake inhibitors. Subsequent research by Barbara Milrod and her colleagues suggests that psychoanalytic psychotherapy might be effective in relieving panic attacks, however, those results alone should be addressed with care. While the results obtained in joint treatments that include cognitive behavioral therapy and selective serotonin reuptake inhibitors are corroborated by many studies and meta-analysis, those obtained by Barbara Milrod are not. Scientific reliability of psychoanalytic psychotherapy for treating panic disorder has not yet been addressed. Specifically, the mechanisms by which psychoanalysis reduces panic are not understood; whereas cognitive-behavioral therapy has a clear conceptual basis that can be applied to panic. The term "anxiolytic" has become nearly synonymous with the benzodiazepines because these compounds have been, for almost 40 years, the drugs of choice for stress-related anxiety.

There are various treatments available to calm racing thoughts, some of which involve medication. One type of treatment involves writing out the thoughts onto paper. Some treatments suggest using activities, such as painting, cooking, and other hobbies, to keep the mind busy and distract from the racing thoughts. Exercise may be used to tire the person, thereby calming their mind. When racing thoughts are anxiety induced during panic or anxiety attacks, it is recommended that the person wait it out. Using breathing and meditation techniques to calm the breath and mind simultaneously is another tool for handling racing thoughts induced by anxiety attacks. Mindfulness meditation has also shown to help with racing thoughts by allowing practitioners to face their thoughts head-on, without reacting.

While all of these techniques can be useful to cope with racing thoughts, it may prove necessary to seek medical attention and counsel. Since racing thoughts are associated with many other underlying mental illnesses, such as bipolar disorder, anxiety disorder, and ADHD, medications used commonly to treat these disorders will help calm racing thoughts in patients.

Treatment for the underlying causes of racing thoughts is helpful and useful in order to calm the racing thoughts more permanently. For example, in people with ADHD, medications used to promote focus and calm distracting thoughts, will help them with their ADHD. Also, people with insomnia who have resulting racing thoughts will find Sleep Apnea treatment & Nasal surgery helpful to eliminate their racing thoughts. It is important to look at the underlying defect that may be causing your racing thoughts in order to prevent them long-term.

Anxiety disorder, the most common mental illness in the United States, affects 40 million people, ages 10 and older; this accounts for 18% of the U.S. population. Most people suffering from anxiety disorder report some form of racing thoughts symptom

The prevalence of OCD in every culture studied is at least 2% of the population, and the majority of those have obsessions, or racing thoughts. With these reportings, estimates of more than 2 million people in the United States (as of 2000) suffer from racing thoughts.

Treatment is dependent on the underlying cause, whether it is organic or psychological in origin. If depersonalization is a symptom of neurological disease, then diagnosis and treatment of the specific disease is the first approach. Depersonalization can be a cognitive symptom of such diseases as amyotrophic lateral sclerosis, Alzheimer's, multiple sclerosis (MS), neuroborreliosis (Lyme disease), or any other neurological disease affecting the brain. For those suffering from depersonalization with migraine, tricyclic antidepressants are often prescribed.

If depersonalization is a symptom of psychological causes such as developmental trauma, treatment depends on the diagnosis. In case of dissociative identity disorder or DD-NOS as a developmental disorder, in which extreme developmental trauma interferes with formation of a single cohesive identity, treatment requires proper psychotherapy, and—in the case of additional (co-morbid) disorders such as eating disorders—a team of specialists treating such an individual. It can also be a symptom of borderline personality disorder, which can be treated in the long term with proper psychotherapy and psychopharmacology.

The treatment of chronic depersonalization is considered in depersonalization disorder.

A recently completed study at Columbia University in New York City has shown positive effects from transcranial magnetic stimulation (TMS) to treat depersonalization disorder. Currently, however, the FDA has not approved TMS to treat DP.

A 2001 Russian study showed that naloxone, a drug used to reverse the intoxicating effects of opioid drugs, can successfully treat depersonalization disorder. According to the study: "In three of 14 patients, depersonalization symptoms disappeared entirely and seven patients showed a marked improvement. The therapeutic effect of naloxone provides evidence for the role of the endogenous opioid system in the pathogenesis of depersonalization."

Brain imaging (functional/structural MRI) may help direct the search for microscopic abnormalities in brain structure and function responsible for late life depression. Ultimately, imaging technologies may serve as tools for early diagnosis and subtyping of depression.