Cara Delevingne is opening up about her shocking drug spiral that led to those infamous post-Burning Man photos -- admitting she had no idea just how serious things had become.

Speaking on "Call Her Daddy," the British model said the shocking 2022 images served as a major wake-up call ... especially because she'd convinced herself she could have one last blowout for her 30th birthday before getting sober.

Cara revealed she was using GHB to knock herself out and cocaine to keep herself awake ... creating a dangerous cycle she couldn't simply walk away from when she decided to quit.

In fact, she says she didn't even realize she needed medical detox and was suffering seizures during the process.

Cara added she'd actually just experienced a seizure around the time those viral photos were taken -- helping explain why they looked so alarming.

As fans know, Cara has since credited that difficult chapter with helping turn her life around ... and today says she's sober and drug-free.