The former Black Eyed Peas member says she "was [suffering from] chemically induced psychosis and dementia" while addicted to crystal meth.
"It took a year after getting off that drug for the chemicals in my brain to settle so that I stopped seeing things. I'd just be sitting there, seeing a random bee or bunny," she recalled to iNews on Thursday.
Fergie's psychosis led her to believe to CSI was following her, so she ran into a church. "They tried to kick me out, because I was moving down the aisles in this crazy way, as I thought there was an infrared camera in the church trying to check for my body," she recalled.
"I bolted past the altar into a hallway and two people were chasing me. I remember thinking, 'If I walk outside, and the SWAT team's out there, I was right all along. 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.' I walked out of the church - obviously, there was no SWAT team. It was just me, in a parking lot. It was a freeing moment," she said.
The 42-year-old says she thinks she has guardian angels watching over her, saying that it's incredible she's even around to tell the story now. "The drugs thing, it was a hell of a lot of fun…until it wasn't. But you know what? I thank the day it happened to me. Because that's my strength, my faith, my hope for something better.
Previously, Fergie opened up about her drug addiction to Time, saying it was "the hardest boyfriend I ever had to break up with."
Fans recently expressed concern regarding the singer's health after she unexpectedly crashed the stage at the TrevorLIVE Gala, but a representative for the star told People, "She's happy and healthy."