Bhutan - I know that memory loss treatment can involve hypnosis or even art therapy.
With patients that suffer from dementia, art therapy is a good form of treatment because they can express themselves freely in the art and the therapist can ask them questions in order to help them understand and possibly improve their cognitive abilities.
They may also have family members bring scrap books so that the patient could be exposed to the past and possibly trigger some memories.
People with dementia do have moments of clarity so this option might also work.
Hypnosis is also great treatment option when the sudden loss of memory is due to a traumatic experience.
In this situation the subconscious mind is blocking out the painful memories as a coping mechanism.
Since a person in this state cannot verbalize the source of their problem, a psychiatrist through the use of hypnosis will be able to determine the source of the pain and create therapeutic treatment options as well as drug therapy in order to help the patient deal with their sudden memory loss.