Shock and denial are typical responses to terrorism, disasters and other kinds of trauma, especially shortly after the event. Both shock and denial are normal protective reactions. Shock is a sudden and often intense disturbance of your emotional state that may leave you feeling stunned or dazed. Denial involves your not acknowledging that something very stressful has happened, or not experiencing fully the intensity of the event. You may temporarily feel numb or disconnected from life.

As the initial shock subsides, reactions vary from one person to another. The following, however, are normal responses to a traumatic event:
Feelings become intense and sometimes are unpredictable. You may become more irritable than usual, and your mood may change back and forth dramatically. You might be especially anxious or nervous, or even become depressed.
Thoughts and behavior patterns are affected by the trauma. You might have repeated and vivid memories of the event. These flashbacks may occur for no apparent reason and may lead to physical reactions such as rapid heartbeat or sweating. You may find it difficult to concentrate or make decisions, or become more easily confused. Sleep and eating patterns also may be disrupted.
Recurring emotional reactions are common. Anniversaries of the event, such as at one month or one year, as well as reminders such as aftershocks from earthquakes or the sounds of sirens, can trigger upsetting memories of the traumatic experience. These ‘triggers’ may be accompanied by fears that the stressful event will be repeated.
Interpersonal relationships often become strained. Greater conflict, such as more frequent arguments with family members and co-workers, is common. On the other hand, you might become withdrawn and isolated and avoid your usual activities. Physical symptoms may accompany the extreme stress. For example, headaches, nausea and chest pain may result and may require medical attention. Pre-existing medical conditions may worsen due to the stress.

When Should I Seek Professional Help?
Some people are able to cope effectively with the emotional and physical demands brought about by a natural disaster or other traumatic experience by using their own support systems. It is not unusual, however, to find that serious problems persist and continue to interfere with daily living. For example, some may feel overwhelming nervousness or lingering sadness that adversely affects job performance and interpersonal relationships.
Individuals with prolonged reactions that disrupt their daily functioning should consult with a trained and experienced mental health professional. Psychologists and other appropriate mental health providers help educate people about normal responses to extreme stress. These professionals work with individuals affected by trauma to help them find constructive ways of dealing with the emotional impact.
With children, continual and aggressive emotional outbursts, serious problems at school, preoccupation with the traumatic event, continued and extreme withdrawal, and other signs of intense anxiety or emotional difficulties all point to the need for professional assistance. A qualified mental health professional can help such children and their parents understand and deal with thoughts, feelings and behaviors that result from trauma.
From the 2001 American Psychological Association.