What is post-traumatic stress disorder and what are its symptoms?

Post-traumatic stress disorder, or PTSD, develops after exposure to a traumatic event involving actual or threatened death, serious injury, or sexual violence. Core symptoms include intrusion symptoms like flashbacks and nightmares, avoidance of trauma-related stimuli, negative changes in thoughts and mood like guilt, detachment, and inability to experience positive emotions, and changes in arousal and reactivity like hypervigilance, exaggerated startle response, irritability, and sleep disturbance. ---