In Flora Rheta Schreiber's book, Sybil puportedly has such an abusive childhood at the cruel hands of her mother that she has been unable to cope with the anxiety that reality has caused her; consequently, her mind has created different personalities that escape the situations in which Sybil finds herself. As she escapes into different personas, Sybil certainly has memory loss because it is another personality that participates in other activities.
Sybil's story begins with her treatment for social anxiety and memory loss. Once the multiple personalities are located, the psychologist begins treatments to recover each personality so that Sybil can become whole.
Curiously, however, it has been discovered that Sybil is actually not a multiple personality, but an extremely suggestible hysteric.