Fergie's addiction to crystal meth didn't just erode her mental health; she also became dangerously thin, at one point weighing a mere 41 kilograms.
Soon after her "dark period", Fergie went on to find fame with the Black Eyed Peas, before launching a successful solo career.
She told iNews that in the early 2000s she suffered from paranoia, "chemically induced psychosis and dementia", the hallucinations becoming so severe that she was convinced the CIA, FBI and SWAT team were tracking her.
She continued: 'I was basically hallucinating on a daily basis. "It took a year after getting after that drug for the chemicals in my brain to settle so that I stopped seeing things", the 42-year-old told the U.K.'s iNews on Thursday, (December 7).
The drugs also caused her to exhibit extreme paranoia; she used to believe that the Central Intelligence Agency and Federal Bureau of Investigation were tracking her, and during one memorable experience, hid from her imaginary pursuers in a church.
She added that when leaving church one day, "I remember thinking: 'If I walk outside, and the SWAT team's out there, I was right all along. I'd just be sitting there, seeing a random bee or a bunny".
Discovering she was alone in the church parking lot was a "freeing moment", the pop star said.
Fergie recounted a similar story before, but it loses no impact in the retelling. Those hallucinations led her to freak out in a church, believing they were after her.
She further said that although the drug phase was "a lot of fun", it was the lowest point in her life. Some of the main short-term side effects include hallucinations, weird and erratic behavior, panic and psychosis among others. She has now reportedly been clean for 18 years. We're family. They're like my work family.
The couple - who have four-year-old son Axl together - called time on their eight-year marriage earlier this year.
As actor Armie Hammer took the stage to introduce the gala's honouree, designer Tom Ford, Fergie appeared to "crash" his speech, interrupting Hammer and making her way to the mic. Her first solo album in over a decade, Double Duchess, is out now.
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