According to Black's Medical Dictionary, 42nd Edition, post-traumatic stress disorder "is one of several psychiatric disorders that can develop in people exposed to ... any event in which there is major loss of life or a threat of loss of life. Most people exposed to trauma do not develop psychiatric disorder; however, some develop immediate distress and, occasionally, the reaction can be delayed for many months. Someone with PTSD has regular recurrences of memories or images of the stressful event (‘flashbacks'), especially when reminded of it. Insomnia, feelings of guilt and isolation, an inability to concentrate and irritability may result."
PTSD is also often accompanied by depression or other emotional symptoms.
The library has several books to learn more about PTSD. Here are a few: