Rich Homie Quan on that LEAN...

We may know what caused Rich Homie Quan's seizures -- lean.

TMZ has a photo of Quan double-cupping just days before he was hospitalized. A source says he'd been on a heavy binge before hitting the studio, then stopped cold turkey three days before he collapsed.

As we've reported, Quan is taking some time off before getting back to work. No word on whether that time will include a rehab stint.