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National Institutes of Health
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What is post-traumatic stress disorder, or PTSD?

PTSD is an anxiety disorder that some people get after seeing or living through a dangerous event.

When in danger, it’s natural to feel afraid. This fear triggers many split-second changes in the body to prepare to defend against the danger or to avoid it. This “fight-or-flight” response is a healthy reaction meant to protect a person from harm. But in PTSD, this reaction is changed or damaged. People who have PTSD may feel stressed or frightened even when they’re no longer in danger.