Response to horror. I agree with dr. Rao about feeling shock, bewilderment, and fear when seeing something disturbing like mutilation and murder. The person also often feels helpless -- not able to do anything in the situation. Also, some have dissociative symptoms: numbness, detachment, decreased emotional responsiveness; reduced awareness of surroundings; derealization; depersonalization; sometimes amnesia too.
Familiar. Today's psychiatrists emphasize resiliency. Everybody knows what sudden emotional shock feels like. My seeing a fatal, dismembering car wreck as a kid made me cherish life -- good thing. Most people do not develop any lasting damage (ptsd, flashbacks, preoccupation); if so, it's manageable. A "therapist" who tells you, "this must have damaged you terribly" is likely to make things worse.
Shock. Shock, bewilderment, anxiety, depression, fear, nightmares, crying spells etc ptsd symptoms may occur later.