EXCLUSIVE: The Brutal Secrets Behind Making of Sally Field's Schizophrenia Drama — And How Hollywood Icon Had to Embody SIXTEEN Different Personalities for Bruising Part

Sally Field starred in the title role of the 1976 two-part made-for-TV movie Sybil, based on a real psychiatric patient with 16 separate personalities... but she needed to channel only one to win the role, RadarOnline.com can reveal.

Director Daniel Petrie had auditioned a slew of actresses and was ready for a lunch break when Field's agent cajoled him into letting her try out. Iconic Joanne Woodward, who was already cast as Dr. Cornelia Wilbur, decided to stick around for the reading.

As Field took on one of Sybil's more prominent personalities – Peggy, a nine-year-old who experiences various triggers to abuse screenwriter Stewart Stern recalled: "I heard this voice that I'd never heard before tearing at me. It al Sybil was a totally different person."

The transformation was so shocking that Woodward dropped her script. The real-life Sybil – revealed in 1998 to be maternal child abuse victim Shirley Ardell Mason, an art teacher who died that year at the age of 75 in Lexington, Kentucky – later called Stern to tell him Field was the only person who could play "the Peggys."

The NBC TV movie is based on the bestselling book of the same name by Flora Rheta Schreiber, who took the name Sybil from the Greek mythological woman prophets called the sibyls, who spoke with multiple voices.

Among the actresses considered for the title role were Lily Tomlin, Natalie Wood, and Audrey Hepburn, who declined the part. Even Woodward was considered as she had played multiple personalities in 1957's The Three Faces of Eve, but she turned it down and asked to play the doctor instead.

Sybil's most dominant personality is Vickie, a French-speaking 18-year-old who is aware of all the personalities and knows everything the others do. She is the only one able to undergo hypnosis.

The others include Vanessa, an outgoing 12-year-old; Marcia, a death-obsessed young girl who dresses in black and tries to kill herself; Ruthie, an infant who cannot move or speak and comes out when Sybil is very frightened; Mary, a symbol of Sybil's beloved late grandmother; and the pale, timid 5- to 6-year-old Sybil Ann.

Then there are religious fanatic Nancy, religious Clara, timid young teen Helen, and party-loving 10- to 11-year-old Marjorie.

Sybil also has two male personalities: Mike, a brash young carpentry buff who builds bookcases for her apartment, and Sid, who likes sports and wants to be like Sybil's dad when he grows up.

In the movie, Sybil signals a return to her core personality by putting on her glasses.

The 198-minute film received high ratings and won four Emmys, including for Field and for Outstanding Special. But it was released years later on VHS in two shorter cuts, running 122 minutes and 132 minutes – both versions trim Sybil's introduction to some of her 16 personalities. The DVD includes the entire movie.

Field is proud that Sybil delved into mental illness at a time when it was seldom discussed openly. Said the two-time Oscar winner: "It opened a dialogue that came flooding out."

The star herself says she was abused and kept a journal she calls "cathartic" while filming Sybil. Field revealed: "Acting was the way I survived. Acting was my Dr. Wilbur. It was the only place I could be me."

In the years since, some experts have doubted the real-life tale. Debbie Nathan penned the 2011 book Sybil Exposed, in which she said most of the story was based on lies and the real woman discovered her personalities under the influence of drugs and alcohol.

While the real Sybil tried to set the record straight by claiming: "I do not really have any multiple personalities," the real Dr. Wilbur dismissed the claim as an attempt to get out of further therapy.