Okay, so I just read this thread in one sitting, there may have been something I missed, so sorry if this was covered before. And sorry these are kinda vague questions.
Is the deja vu a lot like that of dreaming? I don't know that others' dreams are like mine, but when I'm dreaming I'll treat a lot of happenings and media within the dream world as though I remember them and that they've always existed/happened that way. Then, when I wake up, I'll be like No, I've never been RoboCop with my legs cut off at the knees! Not in a previous dream or otherwise! The reason I specifically wonder if it's like dreams is because salvia - the closest I've had to nitrous, being a short lasting, intense, legal dissociative - always reminds me of dreams in so many aspects.
Also, when stacking on a psychedelic, would cannabis provide something close to that special augmentation you've mentioned with other combos? I know it's not the class of psychedelic that you guys seem to mean, but I've been pretty good about pacing myself with grass recently and can get put in a distinctly different world when vaping a whole bowl at once after a week's break. It's definitely more happy and "dumbed down" than LSD, but I wonder if it'd help any all the same.