Post-Traumatic Stress Disorder (PTSD)

Post-traumatic stress disorder (PTSD) can develop in some people after a terrifying event that involved physical harm or the threat of physical harm. A person who develops PTSD may have experienced the event first-hand, or may have witnessed the event happening to someone or something else. PTSD causes people to startle easily, become emotionally numb, lose interest in things they used to enjoy, have trouble feeling affection, be irritable, become more aggressive, or even become violent. They avoid situations that remind them of the original incident, and anniversaries of the incident are often very difficult. Many people with PTSD relive the trauma over and over in their thoughts during the day and in nightmares when they sleep.
For More Information:

Adults:

http://www.aacap.org/cs/root/

Adolescents:
http://www.kidshealth.org/teen/your_mind/mental_health/ptsd.html