Fergie's addiction to crystal meth was so bad that at one point she was hallucinating "daily".
The 42-year-old singer struggled with her addiction to the drug prior to finding fame in the Black Eyed Peas, and labelled it the "lowest point" of her life.
"I was (suffering from) chemically induced psychosis and dementia. I was hallucinating on a daily basis," she told iNews. "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."
Recalling one particular incident where her paranoia was at an all-time high, Fergie explained she thought the "CIA, FBI and a SWAT team" were tracking her, so she decided to attempt to seek refuge in 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. I bolted past the altar into a hallway and two people were chasing me," she said.
"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 anymore, 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."
Fergie is now at a much happier point in her life, as she's healthy, successful and mother to four-year-old son Axl with estranged husband Josh Duhamel. And now she can look back at the drug stage of her life with a clear mind, the Double Dutchess star is thankful that she had the strength to kick her habit.
"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," she explained.