Post-traumatic stress disorder (PTSD) is a psychological and physical condition that can be caused by extremely frightening or distressing events.

PTSD can occur after experiencing or witnessing traumatic events such as military combat, natural disasters, serious accidents, terrorist attacks, violent deaths and personal assaults, including rape and other situations in which the person felt extreme fear, horror or helplessness.

Many people develop PTSD because someone close to them died suddenly (around 40%). Around 30% of people exposed to such a stressful event will develop PTSD.

PTSD can affect anyone. It's common and affects around 5% of men and 10% of women some time in their life. It can happen at any age, including in childhood. An individual with PTSD often relives the experience through nightmares and flashbacks, and has problems with concentrating and sleeping, with feelings of isolation and detachment from life. These symptoms can be lasting and severe enough to impair the person's daily life significantly.

Symptoms usually develop immediately or within three months of a traumatic event, although, occasionally, they do not begin until years later.

PTSD has been called shell shock or battle fatigue syndrome because it first came to prominence in the First World War, with soldiers' memories of the trenches. It has only recently been recognised that traumatic events outside conflict situations can have similar effects.

The term post-traumatic stress disorder was first used after the Vietnam War. It was formalised in 1980 when it was included in the Diagnostic and Statistical Manual of Mental Disorders, which was developed by the American Psychiatric Association.