From The Sidran Institute:

“Dissociation is a disconnection between a person’s thoughts, memories, feelings, actions, or sense of who he or she is. This is a normal process that everyone has experienced. Examples of mild, common dissociation include daydreaming, highway hypnosis, or ‘getting lost’ in a book or movie, all of which involve ‘losing touch’ with awareness of one’s immediate surroundings. …

“During a traumatic experience … dissociation can help a person tolerate what might otherwise be too difficult to bear. In situations like these, a person may dissociate the memory of the place, circumstances, or feelings about the overwhelming event, mentally escaping from the fear, pain, and horror. This may make it difficult to later remember the details of the experience, as reported by many disaster and accident survivors. …

“Because it is so effective, children who are very practiced at dissociating may automatically use it whenever they feel threatened—even if the anxiety-producing situation is not extreme or abusive. Even after the traumatic circumstances are long past, the left-over pattern of defensive dissociation sometimes remains into adulthood. Habitual defensive dissociation may lead to serious dysfunction in school, work, social, and daily activities.”