I had a colonoscopy last year and I remember feeling conscious but absolutely powerless, it was like watching a video of myself. After the procedure, I complained to the surgeon that he hadn't come into the recovery room to talk to me, and he said he had. He even showed me a video of him talking to me. He said he had given me a drug which was very similar to a date rape drug, and this erases short term memory so he always videos himself talking to patients as they never remember. So I don't know if burundanga is actually a thing, but I do know that there are drugs out there which render you helpless but conscious and then wipe your short term memory.
There are enough stories, mainly in Colombia, of burundanga for it to be a thing, I'm sure at least some of them must be true.