Agatha Christie and her unsolved mystery

Agatha Christie is one of the best known and best selling novelists of all time. Her books have sold over a billion copies worldwide and she is well loved by all her fans. Agatha however had a mystery of her own. On the 3rd December 1926 she disappeared for 11 days only to reappear with no memory of what happened. What really happened to Agatha in those 11 days?