Amnesia is the inability to recall past events. Amnesia can result from physical trauma (such as being in an accident and getting a blow to the head) or from psychological problems. One type of amnesia, dissociative amnesia, is the inability to recall events that results from psychological problems, specifically from too much stress. This is sometimes seen in victims of horrible events such as violent crimes, murder, war, etc. It is not a typical situation, but sometimes when an event is simply too difficult for a person to handle, they protect themselves by blocking the memory of the event. In these cases the problem is usually temporary.