Amnesia is memory loss that may be caused by a head injury or stroke, substance use, or a severe emotional event, such as combat or a car crash. Depending upon the cause, amnesia may be temporary or it may be a permanent condition.

Amnesia can involve complete loss of memory of one or more of the following:

• Personal identity
• Events or circumstances
• A specific period of time
• An entire lifetime

Amnesia can also involve not being able to make new memories. Someone may not be able to remember things that happen after the event that caused amnesia.

The cause determines whether the condition comes on slowly or suddenly. Memory problems that come on gradually may be a part of ongoing mental decline (dementia). Transient global amnesia is a type of unexplained amnesia that begins suddenly.

Treatment options and results of treatment of amnesia depend on the cause of lost memory.