Post traumatic stress disorder (PTSD) describes anxiety that is caused by memories of a past traumatic experience. The experience is usually a severe trauma that was a threat to the person's life or someone else's life. However, any event that generates extreme fear, horror or helplessness could result in PTSD.

Examples include:

• Diagnosis of a life-threatening condition
• Natural disasters
• Severe automobile accidents
• Violent personal assaults
• War

The person who has PTSD reexperiences the traumatic event in some way. These episodes are commonly called flashbacks.

Flashbacks may involve:

• Hallucinations
• Images
• Dreams
• Delusions
• Similar feelings to those that occurred during the event

These intense flashbacks cause the person to avoid any thoughts, feelings or situations that might remind them of the event. Avoiding the flashbacks may cause the person to be irritable, be easily startled, lose concentration and suffer from insomnia.