Amnesia is the loss of memories, usually caused by an injury to the brain, illness, or psychological trauma. Someone with amnesia might forget who they are, where they live, or important events from their past. In movies, a character often gets bonked on the head and wakes up with amnesia, unable to remember anything, but real amnesia rarely works quite that dramatically.

There are different types of amnesia. Retrograde amnesia means forgetting things that happened before the injury: you might not remember the accident that caused your concussion or even the weeks leading up to it. Anterograde amnesia means having trouble forming new memories after the injury: you might meet someone today but not remember meeting them tomorrow.

Most amnesia is temporary. A person who suffers a concussion might experience some memory loss but regain most or all of their memories as they heal. However, severe brain injuries or certain diseases can cause permanent amnesia.

While amnesia is a real medical condition that can be frightening and disorienting for those who experience it, doctors and researchers continue learning more about how memory works and how to help people recover memories when possible.