Earlier this year, Fergie also revealed that she was no longer a member of Black Eyed Peas, the multi-million selling hip-hop group for whom she was a vocalist from 2002. She begun the drug habit while performing with Wild Orchid, and her addiction followed her after she left the band in 2001.
Speaking to i Newspaper: "At my lowest point, I was [suffering from] chemically-induced psychosis and dementia".
"I was hallucinating on a daily basis".
"It took a year after getting off that drug for the chemicals in my brain to settle so that I stopped seeing things", the mother to Axl, 4 (with Duhamel), continued. "I'd just be sitting there, seeing a random bee or a bunny".
Fergie became convinced that the CIA, FBI, and SWAT teams were after her, leading to an embarrassing incident in church.
Catholic-raised Fergie, whose real name is Stacy Ann Ferguson, eventually sought help in a church.
"They tried to kick me out, because I was moving down the aisles in this insane way, as I thought there was an infrared camera in the church trying to check for my body. I bolted past the altar into a hallway and two people were chasing me", she said. But if they're not out there, then it's the drugs making me see things and I'm going to end up in an institution. "And if it really is the drugs, I don't want to live my life like this any more, anyway'. It was a freeing moment".
She explained "The drugs thing, it was a hell of a lot of fun... until it wasn't".
Her candid conversation comes after she admitted she could not have predicted her split from Josh Duhamel.
"Both Josh and I are working full-time right now. That's why we wanted to find our footing with our separation before we announced it publicly: to make sure we really got it together for our kid", she said.
Her second solo album arrived this September, a massive 11 years after her previous record The Dutchess in 2006.