Memory loss, also referred to as amnesia, is an abnormal degree of forgetfulness and/or inability to recall past events. Depending on the cause, memory loss may have either a sudden or gradual onset, and memory loss may be permanent or temporary. Memory loss may be limited to the inability to recall recent events, events from the distant past, or a combination of both. Although the normal aging process can result in difficulty in learning and retaining new material, normal aging itself is not a cause of significant memory loss unless there is accompanying disease that is responsible for the memory loss.
Transient global amnesia is a rare, temporary, complete loss of all memory. Anterograde amnesia refers to the inability to remember recent events in the aftermath of a trauma, but recollection of events in the distant past in unaltered. Retrograde amnesia is the inability to remember events preceding a trauma, but recall of events afterward is possible.
Memory loss has multiple causes including a number of chronic medical and psychological conditions, trauma, medications, drug or alcohol abuse, and infections.