The September 11, 2001 terrorist attacks on the United States had a profound effect on people of all ages. In the month following  September 11, the number of prescriptions for anti-anxiety medication increased over 20%. Chronic diseases that were previously well managed and under control were exacerbated intensely by the stress and anxiety created by the attacks.
(Okie, S. Use of Anti-Anxiety Drugs Jumps in U.S. Washington Post, Oct 14, 2001.)

A study released in May 2002, estimated that more than 400,000 New Yorkers experienced PTSD after September 11.  Many are still experiencing PTSD symptoms. (AP Worldstream. Study says that more than 400,000 New Yorkers experienced post-traumatic stress disorder after Sept. 11 2002:May 18.)

A study of stress reactions not just in New York but also throughout the country shortly after September 11, reported in the New England Journal of Medicine, found that 90% of those sampled nationwide experienced increased levels of stress, and 44% experienced at least one of five substantial stress symptoms.

The study concluded that even people who where not present at the traumatic event experienced stress. The authors further suggest that the psychological effects of this terrorism is not likely to disappear soon, and that clinicians who practice even in regions that are far from the attacks should be prepared to assist people with trauma-related symptoms of stress.
(Schuster MA, Stein BD, Jaycox LH et al. A national survey of stress reactions after the September 11, 2001 terrorist attacks. New England Journal of Medicine. 2001;345:1507-1512.)

With two to three times the normal incidence of PTSD, and it being a condition that can last a lifetime, the trauma of September 11, 2001 has the potential of creating a substantial public health problem.