neurosis, in psychiatry, a broad category of psychological disturbance, encompassing various mild forms of mental disorder. Until fairly recently, the term neurosis was broadly employed in contrast with psychosis, which denoted much more severe, debilitating mental disturbances. The two terms were used regularly until 1980, when the American Psychiatric Association released a precise listing of known mental disorders excluding the two broad categories of "mild" and "serious" mental disorders.

Neurosis, according to Sigmund Freud, arose from inner conflicts and could lead to anxiety. In his formulation, the causal factors could be found roughly in the first six years of life, when the personality, or ego, is weak and afraid of censure. He attributed neurosis to the frustration of infantile sexual drives, as when severe eating and toilet habits and other restrictions are parentally imposed (see Oedipus complex), which appear in adulthood as neurotic symptoms (see psychoanalysis). Other authorities have emphasized constitutional and organic factors. Among the psychoanalysts, Alfred Adler and H. S. Sullivan stressed social determinants of personal adjustment, and Karen Horney emphasized insecurity in childhood as causes of neurosis.

Until 1980, neuroses included anxiety disorders as well as a number of other mild mental illnesses, such as hysteria and hypochondria. Anxiety disorders are fairly common, and generally involve a feeling of apprehension with no obvious, immediate cause. Such intense fears of various situations may be severe enough to prevent individuals from conducting routine activities. Phobias, the most common type of anxiety disorder, involve specific situations which cause irrational anxiety attacks. For instance, an individual with agoraphobia (fear of open spaces) may be too anxious to leave their house. Obsessive-compulsive disorder occurs when an individual relentlessly pursues a thought or action in order to relieve anxiety. Panic disorder is characterized by anxiety in the form of panic attacks, while generalized anxiety disorder occurs when an individual experiences chronic anxiety with no apparent explanations for the anxiety. Post-traumatic stress disorder, occurring in the wake of a particularly traumatic event, can lead to severe flashbacks and a lack of responsiveness to stimuli. Anxiety disorders are usually accompanied by a variety of defense mechanisms, which are employed in an attempt to overcome anxiety. Hypochondriasis and hysteria (now generally known as conversion disorder) are classified today as somatoform disorders, and involve physical symptoms of psychological distress. The hypochondriac fears that minor bodily disturbances indicate serious, often terminal, disease, while the individual suffering from conversion disorder experiences a bodily disturbance—such as paralysis of a limb, blindness, or deafness—with no clear biological origin. Treatment of neurosis may include behavior therapy to condition an individual to change neurotic habits, psychotherapy, and group psychotherapy. Various drugs may also be employed to alleviate symptoms.

Mental disorder in which an individual experiences obsessions or compulsions, either singly or together. An obsession is a persistent disturbing preoccupation with an unreasonable idea or feeling (such as of being contaminated through shaking hands with someone). A compulsion is an irresistible impulse to perform an irrational act (such as repeatedly washing the hands). The two phenomena are usually, but not always, linked in the obsessive-compulsive person. Onset of the illness has been linked to malregulation of the neurotransmitter serotonin as well as to the ill effects of high stress.

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Mental and emotional disorder that affects only part of the personality, is accompanied by a less distorted perception of reality than in a psychosis, and is characterized by various physiological and mental disturbances (such as visceral symptoms and impaired concentration). The neuroses include anxiety attacks, certain forms of depression, hypochondriasis, hysterical reactions, obsessive-compulsive disorders, phobias, various sexual dysfunctions, and some tics. They have traditionally been thought to be based on emotional conflict in which a blocked impulse seeks expression in a disguised response or symptom. Behavioral psychologists regard them as learned, inappropriate responses to stress, which can be unlearned.

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