Beehived diva, infamous for her drug and booze intake, went cold turkey on her heavy drinking in the month before her death on Saturday - and family members think her decision was fatal.
"Abstinence gave her body such a fright, they thought it was eventually the cause of her death," a family friend told British newspaper The Sun.
Her father, Mitch, believed "the shock of giving up, after everything she had been through over a bad few years, was just too much for her to take," the friend said.
Doctors had advised the 27-year-old "Rehab" singer to cut back gradually on her boozing, according to The Sun.
On Tuesday, hundreds of teary mourners said farewell to Winehouse at a London funeral at the Edgwarebury Cemetery. The Grammy-winning singer finally found peace after a tumultuous life of endless drama, her father said in a eulogy at the private service.
"He stressed so many times she was happier now than she had ever been and he spoke about her boyfriend and paid tribute to a lot of people in her life," said family spokesman Chris Goodman.
The funeral featured prayers, song and laughter as her father spoke before the mourners harmonized on Carole King's "So Far Away" - a Winehouse favorite.
"Good night, my angel, sleep tight," said dad Mitch Winehouse, a cabbie/jazz singer. "Mummy and Daddy love you so much."
Family sources say Amy died after ignoring her doctor's advice to cut down on her heavy drinking gradually.
And the tragic star's loved ones believe she was killed by a seizure because her tiny 4ft 11in frame could not cope with such a dramatic withdrawal.
A source close to Amy's family said: "Abstinence gave her body such a fright they thought it was eventually the cause of her death."
The Rehab singer, found dead on Saturday aged 27, fell off the wagon three days earlier, sinking gin and Red Bull mixes at the iTunes festival at the Roundhouse in Camden, North London.
But in his eulogy at her funeral on Tuesday, her cabbie father Mitch dismissed reports she went on a 72-hour bender.