Post-traumatic stress disorder (PTSD) is an anxiety disorder caused by very stressful, frightening or distressing events.
Someone with PTSD often relives the traumatic event through nightmares and flashbacks, and may experience feelings of isolation, irritability and guilt.
They may also have problems sleeping, such as insomnia, and find concentrating difficult.
These symptoms are often severe and persistent enough to have a significant impact on the person's day-to-day life.
Any situation that a person finds traumatic can cause PTSD.
These can include:
serious road accidents
violent personal assaults, such as sexual assault, mugging or robbery
serious health problems
PTSD can develop immediately after someone experiences a disturbing event, or it can occur weeks, months or even years later.
PTSD is estimated to affect about 1 in every 3 people who have a traumatic experience, but it's not clear exactly why some people develop the condition and others do not.
People who repeatedly experience traumatic situations, such as severe neglect, abuse or violence, may be diagnosed with complex PTSD. Complex PTSD can cause similar symptoms to PTSD and may not develop until years after the event.
It's often more severe if the trauma was experienced early in life, as this can affect a child's development.
It's normal to experience upsetting and confusing thoughts after a traumatic event, but most people improve naturally over a few weeks.
PTSD can be successfully treated, even when it develops many years after a traumatic event.
Any treatment depends on the severity of symptoms and how soon they occur after the traumatic event.
Any of the following treatment options may be recommended:
watchful waiting – monitoring your symptoms to see whether they improve or get worse without treatment
antidepressants – such as paroxetine or mirtazapine
Cognitive behavioural therapy (CBT)