A Neurosis is a generally mild form of mental illness manifesting as unease or distress in response to a specific stimulus. Most people have some form of neurosis, which can be triggered by almost anything. Common phobias, like arachnophobia (fear of spiders) are a form of neurosis and can be mild or severe depending on the reaction.
Sigmund Freud, the father of modern psychology, considered many mental issues to be the result of the Ego repressing the Id, with the repression manifested as symptoms of neurosis. In his model, the neurosis itself takes the place of either the memory of trauma or acceptance of past events; "curing" the neurosis meant accepting the past as fact and removing it from unconscious obsession. Freud also talked about "transfer neuroses," which occur when a person transfers desire for something or someone into a behavior or habit; the conscious or unconscious desire cannot be satisfied, and so the neurosis forms in response, replacing the desire with a feeling or action.
The American Diagnostic and Statistical Manual of Mental Disorders (DSM) has eliminated the category of "Neurosis", reflecting a decision by the editors to provide descriptions of behavior as opposed to hidden psychological mechanisms as diagnostic criteria.
This change shows that the older model of repressed memories or events has not been borne out by actual studies; the symptomatic approach of classifying neuroses instead of treating the patient may result in magnification of the neurosis, or in worse cases increased distress or new neuroses.