The main types of amnesia are:

Anterograde amnesia: People who find it hard to remember ongoing events after suffering damage to the head. They do not tend to forget their childhood or who they are, but have trouble remembering day-to-day events.

Retrograde amnesia:People who find it hard to retrieve memories prior to an incident in which they suffer damage to the head. Sometimes people never remember the seconds leading up to the incident.

Korsakoff's psychosis: Memory loss caused by alcohol abuse. The person's short-term memory may be normal, but they will have severe problems recalling a simple story, lists of unrelated words, faces and complex patterns.

This tends to be a progressive disorder and is usually accompanied by neurological problems, such as uncoordinated movements and loss of feeling in the fingers and toes. If these symptoms occur, it may be too late to stop drinking.

Traumatic amnesia: This follows brain damage caused by a severe non-penetrative blow to the head, such as in a road accident. It can lead to anything from a loss of consciousness for a few seconds to coma.

Infantile/childhood amnesia:This refers to a person's inability to recall events from early childhood. There are many theories on this, for example, Freud put it down to sexual repression. Others say it could be linked to language development or the fact that some areas of the brain linked to memory are not fully mature.

Hysterical amnesia (also known as fugue amnesia):This covers episodes of amnesia linked to psychological trauma. It is usually temporary and can be triggered by a traumatic event with which the mind finds it difficult to deal. Usually, the memory slowly or suddenly comes back a few days later, although memory of the trauma may remain incomplete.

Treatment varies according to the type of amnesia and the suspected cause.

Anyone suffering any symptoms of amnesia should seek medical attention.