Final answer:
Intense feelings of fear, helplessness, or horror are key signs of Posttraumatic Stress Disorder (PTSD), an anxiety disorder caused by experiencing severe psychological trauma.
Step-by-step explanation:
Intense feelings of fear, helplessness, or horror are key signs of Posttraumatic Stress Disorder (PTSD). PTSD is an anxiety disorder triggered by exposure to a terrifying event or ordeal in which there was potential for or actual occurrence of grave physical harm.
It can manifest through various symptoms including intrusive and painful memories, jumpiness, negative emotional states, detachment from others, and avoidance of reminders of the traumatic event. This disorder was particularly noted among American GIs during the Vietnam War, though it was not well understood or treated at the time.