Since 9/11, many mental health researchers and professionals have been learning more about how such disasters or traumatic events can affect one's mental health. The article "The Changing Mental Health Aftermath of 9/11" , originally written in 2011 (a decade after 9/11), highlights some of what has been discovered including how "'the mental health toll of disasters and terrorism is not limited to post-traumatic stress disorder.' They can also trigger major depressive disorder, generalized anxiety disorder, complicated grief (recognized in the mental health world as being unusually strong and long-lasting), substance abuse and a host of other symptoms that might come and go over time."
The article also recognizes how the anniversaries of these events can be a difficult and emotionally challenging time, in addition to exploring how the psychological "first aid" protocol for handling large-scale traumatic events has evolved over time. Definitely worth a read!