Post-traumatic stress disorder occurs when a person who has gone through a significant trauma, a life-threatening accident, a natural disaster, or abuse shows stress symptoms that impair the person's ability to function. Psychosomatic disorder is a real, physical disorder that has a psychological cause. Tension headaches have real pain caused by muscle spasm, but stress and anxiety have a role in causing the symptoms. Schizophrenia is a form of psychosis in which there is a loss of contact with reality. MRI and PET scans show brain abnormalities and changes in function. Panic disorder runs in families, but whether it is due to genetics or environment is not clear. Panic disorder is characterized by sudden, brief attacks of intense fear that cause physical symptoms. Epileptic-like activity in the brain is thought to be the cause of intermittent explosive disorder which is characterized by recurrent episodes of aggression toward people or property.

All of these are factors that can contribute to PTSD, except for an on-going chronic physical health condition. On-going mental health conditions, such as depression and anxiety, can contribute to PTSD (usually in combination with more actue problems of experiencing or witnessing trauma), and physical conditions can increase the likelihood of depression, but alone, they do not increase the likelihood of developing PTSD.

Individuals with a panic disorder suffer from sudden, overwhelming and repeated attacks of terror, which can occur out of nowhere. Major changes in behavior and persistent anxiety over having further attacks are characteristic of panic disorders. Often external stimuli or internal thoughts can trigger these attacks.

The other choices are incorrect. The fear of no escape possibilities in crowded situations is considered to be one criteria of agoraphobia, not of panic disorder. The exaggerated fear of specific objects or situations is characteristic for phobic disorders, not of panic disorder. Last, generalized anxiety disorder is marked by the diffuse state of general worries and fears, which are not based on a specific object or event. This is not the best description listed to fit the characteristics for panic disorder.

Agoraphobia occurs when a patient fears situations that make them feel trapped, embarrassed, or helpless. They may fear an actual event or even simply the anticipation of an event. This is more likely to occur in a crowded area, such as a subway or metro bus, than it would simply interacting with a few strangers at a given time. In other words, they may experience a lack of desire to interact with strangers to avoid embarrassment, but that is not a situation in which they would feel trapped or helpless.

Social anxiety disorder is the correct answer. The fear is judged to be out of proportion to the actual risk of the social interactions and is causing significant impairment in occupational functioning, which is concerning for social phobia. Social anxiety disorder should be suspected when intense fear of social interactions, in which the individual may be scrutinized by others, is out of proportion to the actual threat of the social situation and causes significant impairment in important areas of functioning, and the fear is not better explained by some other mental disorder.

In obsessive-compulsive disorder (OCD), patients have obsessions and compulsions. The obsessions are recurrent thoughts, fears, images, or impulses. The compulsions are recurrent, irresistible actions such as counting, hand washing, or systematically arranging things. People with schizophrenia have hallucinations and suffer from delusions. When there is no identifiable physical cause to explain physical symptoms, a somatoform disorder may be the diagnosis. People who lie, cheat, steal, and have no sense of responsibility exhibit the symptoms of antisocial personality disorder. Impulse control disorders are an inability to resist an impulse to perform an act that is harmful to the individual or others. Substance abuse and chemical dependence fall under this category.

People with obsessive-compulsive disorder often feel the need to perform certain rituals or routines repeatedly. These individuals are often compelled by intrusive thoughts. An individual compelled to perform repeated behavior, such as continually locking and unlocking a door, will often feel distressed by these intrusive thoughts and the need to perform certain behaviors. Someone with obsessive-compulsive disorder cannot simply feel dismissive toward these thoughts, which is part of the distress they experience. While performing these rituals can sometimes cause a temporary sense of relief, this relief does not last for the rest of the day. It is only a transient sense of relief that may come from temporarily satisfying the intrusive thoughts. An individual compelled to perform repeated behavior would have no particular reason to feel content or relaxed.

Trichotillomania is associated with irresistible urges to perform unwanted repetitive behavior, which falls under the obsessive-compulsive spectrum. Although the disorder may cause anxiety to an individual, it does not fit on the anxiety spectrum of behavioral disorders. The autism and bipolar disorder spectrums do not include behaviors or characteristics that are associated with trichotillomania.

Obsessive compulsive disorder, or OCD, is related to a decrease in bioavailable "serotonin" levels. This may be due to alterations serotonin transporter (SERT) function, which increase SERT activity, thus clearing serotonin from the synaptic cleft more rapidly and leading to a shorter duration of effect. While any of the other signaling molecules listed may affected in OCD, serotonin is the only neurotransmitter known to have a direct association with the disorder.

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.