In the context of obsessive compulsive disorder, an obsession refers to "persistent or recurrent involuntary thoughts and/or images which are intrusive and cause marked distress or anxiety." These thoughts often lead to compulsions, or repetitive behavior that an individual feels driven to perform according to rigid rules or rituals.

While it may occur in children under five, obsessive compulsive disorder generally presents either in childhood (age 10-12) or in early adulthood (ages 18-22). Onset after age 25 is less common, and onset in middle age is rare. 

The manic and depressive phases of bipolar disorder can be treated with the mood stabilizer lithium. Lithium is used for the prevention of future depression and suicide and for the prevention of future mania. Schizophrenia is treated with antipsychotic medications. Medications to reduce nightmares, insomnia, and startle reactions are used in the treatment of post-traumatic stress disorder. Benzodiazepines and selective serotonin reuptake inhibitors (SSRIs) are used to treat panic disorders. SSRIs are also used to treat obsessive-compulsive disorder.

Cyclothymic disorder is a mild form of bipolar disorder where a person mood swings over a period of years that go from mild depression to elevated mood and excitement.

Individuals with any form of bipolar disorder will most likely experience some psychotic episodes. During manic episodes, they will have delusions of grandeur, racing ideas and speech, distractibility and high-risk behaviors. They generally sleep and eat less often during these episodes as well. A patient with cyclothymic disorder lacks the vegetative symptoms associated with major depressive disorders. They can concentrate normally and lack both suicidal ideations and feelings of worthlessness when "low."

Borderline personality disorder is a diagnosis in people who are impulsive, unstable in mood, and manipulative. They can be charming and friendly one minute and angry, irritable, and sarcastic the next. People who need to escape from extreme trauma, most often from sexual or physical abuse in childhood, may develop distinct different personalities. This is termed dissociative identity disorder. People who lie, cheat, steal, and have no sense of responsibility and no anxiety of guilt about their behavior are described as having an antisocial personality disorder. People with schizophrenia experience hallucinations and delusions. Generalized anxiety disorder consists of persistent, excessive worrying and uncontrolled anxiety that has lasted for at least six months. 

"Borderline personality disorder" is characterized by difficulty regulating behavior or thoughts, extreme fluctuations in mood, unstable relationships due to idealization or demonization, fear of abandonment or other attachment disorders, and impulsive or reckless behavior.

The other choices are incorrect. "Obsessive-compulsive disorder" is typified by repetitive, unwelcome thoughts that compel the individual to perform ritualistic acts. "Paranoid personality disorder" is a condition of pervasive, long-standing paranoia and general mistrust of others. "Schizotypal personality disorder" is an antisocial disorder: individuals experience social anxiety, the urge to isolate themselves from others, and odd behavior or beliefs.

The DSM IV criteria for diagnosis of borderline personality disorder includes at least five of the following symptoms:

• Extreme reactions to abandonment, real or perceived
• A pattern of tumultuous relationships with family, friends, and romantic interests, often vacillating from extreme idealization to extreme dislike or devaluation.
• Distorted and unstable self-image, which can result in sudden changes in feelings, opinions, values, plans, or goals
• Impulsive and destructive behaviors, such as spending sprees, unsafe sex, substance abuse, reckless driving, and binge eating
• Recurring suicidal behaviors or self-harming behavior
• Intense and highly changeable moods
• Chronic feelings of emptiness and/or boredom
• Inappropriate, intense anger or problems controlling anger
• Having stress-related paranoid thoughts or severe dissociative symptoms, such as feeling cut off from oneself, observing oneself from outside the body, or losing touch with reality.

Schizophrenia is a mental disorder where people perceive things without a stimulation—hallucinations. These people also suffer paranoid delusions, and their behaviors can be totally inappropriate. The development of distinctly separate personalities is called dissociative identity disorder (DID). People with schizophrenia do not have a split personality. People with bipolar disorder alternate between episodes of depression and mania. Trichotillomania is characterized by the repeated urge to pull out body hair. When there is no identifiable physical cause to explain physical disorders that are real to the patient, somatoform disorder may be diagnosed.

People with schizophrenia have hallucinations, delusions, and difficulty concentrating. Symptoms of schizophrenia typically begin to appear in the late teens and twenties. Social phobias involve fear of being embarrassed in social situations. The most common is fear of public speaking. People with generalized anxiety disorder are frightened of something but are unable to speak about a specific fear. They develop physical fear reactions. Alterations of episodes of depression with episodes of mania is called bipolar disorder. The inability to resist and impulse to perform an action that is harmful to the individual or to others is an impulse control disorder. Examples are kleptomania and pyromania.

Affective disorders are a group of disorders marked by a disturbance of mood. Included in the category is major depression. People with major depression see nothing but sorrow in the future and may not wish to live anymore. Anxiety disorders are characterized by unreasonable anxiety or fear that is inappropriate to the circumstances and disrupts the person's life. Psychosomatic disorder is a real physical disorder that has a psychological cause, such as tension headaches. Dissociative disorder is a type of personality disorder that involves a disassociation of past experiences from present memory. The origin of dissociative disorders is a need to escape extreme trauma, usually some form of abuse. Impulse control disorders are an inability to resist an impulse to perform an action that is harmful to others. Includes in this category are kleptomania and pyromania.