The 17 symptoms of PTSD, categorized into four groups, are: Intrusive memories (flashbacks, nightmares, reliving the event, distress at reminders), avoidance (avoiding thoughts or feelings, avoiding reminders), negative changes in thinking and mood (negative thoughts about oneself or others, hopelessness, memory problems, difficulty maintaining close relationships, feeling detached, lack of interest in activities, difficulty experiencing positive emotions), and changes in physical and emotional reactions (being easily startled, always being on guard, self-destructive behavior, trouble sleeping, trouble concentrating, irritability, angry outbursts, overwhelming guilt or shame).