Amnesia is memory loss that may be caused by a head injury or stroke, substance use disorder, 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

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). Total 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.