Oscar winner SALLY FIELD has been crushed by a devastating one-two punch! The star’s beloved mother passed away on Sally’s 65th birthday as she was still reeling from incredible charges that the character in her Emmy-winning role of “Sybil” was a fraud, say sources.

“Sally’s whole world has come crashing in on her,” a longtime family friend told The ENQUIRER.

“The loss of her mother on top of the ‘Sybil’ scandal has left her heartsick. She’s almost inconsolable, and with her history with anxiety it seems as if everyone’s afraid she may do something desperate just to deaden her emotional pain.”

The “Brothers & Sisters” star’s mother Margaret O’Mahoney lost her battle with cancer at age 89 on Nov. 6 with Sally at her side.

During the last months of hermoth­er’s illness, Field regularly flew from Richmond, Va., where she’s playing Abra­ham Lincoln’s wife in the upcoming Steven Spielberg film “Lin­coln,” to her mother’s home in Malibu, Ca­lif., said the source.

“Sally made sure she was at her moth­er’s side every possible second she could, even if it meant taking reg­ular red-eye flights back and forth to Los Angeles,” the friend revealed. “Her mom meant everything to her.”

Watching her mother slip away was heart-wrenching for Sally, said another source.

“Margaret had the best care in the world, but Sally felt so help­less,” the source divulged.

“When she could, Sally slept in the same room with her mother. She’d read to her and stroke her cheeks. After Margaret died, Sally cried for hours.”

While her mother lay dying, Sally was also grappling with her per­sonal humiliation over the shocking new book “Sybil Exposed: The Extraordinary Story Behind the Famous Multiple Personality Case,” by author Debbie Nathan.

The expose alleges that Shirley Mason – the woman on whom Sally’s role in the hit 1976 minise­ries was based – made up the whole story with the help of her psychiatrist and the book’s original author!

“According to the new book, Sybil’s story may have been a hoax,” explained the source.

“Sally is sickened that the minise­ries’ reputation is taking a hit. To hear that one of her most prized roles was based on a sham has crushed her soul. To say she’s devastated would be an understatement.”

Despite her Hollywood success, Sally – who’s twice divorced and the mother of three sons – fought severe bouts of depression that led to binge eating, starvation, passing out and pop­ping diet pills, as The ENQUIRER has previously reported.

“Sally’s dark side has never really been far from the surface. It’s one of the reasons why she’s such an in­credible actress,” noted her friend.

Now Sally – who carried on a pub­lic romance with her “Smokey and the Bandit” co-star Burt Reynolds – is channeling those dark emotions into her role as Mary Todd Lincoln, added the source.

“Mrs. Lincoln lived a morose life of depression and sadness. Some say she was suicidal,” the friend said.

“As a consummate actress, Sally says she’s trying to funnel her sor­row into the role. But those closest to her feel the one-two punch of her mother’s death and the ‘Sybil’ scandal is just too much emotional baggage for her to bear.”

POP FYI: Sally’s mom was known as Margaret Field when she appeared in films including “The Man from Planet X” and her stepdad was Tarzan and stunt man supreme Jock Mahoney (real name O’Mahoney).