Is it possible that your brain makes you forget things as a self defense mechanism?

After hearing several stories of people completely forgetting everything that happened during a tragic incident, i was intrigued about why. The people in these stories had gone through something traumatic like kidnap and torture, witnessing a gruesome death, etc. After the incidents, the people had trouble remembering what happened, why they where there, or when it took place. The doctors that treated them report no head trauma/injury, so they couldn't conceive why they had forgotten everything that happened.