i noticed this after the first time i used a psychedelic. which was mushrooms.
whenever i got blazed not too long after i tripped (usually off of sativa) i noticed mild hallucinations that i had on that previous trip.
i also had what you described with the mind set while on a hallucinogen.
i consider these very mild flashbacks.
once you take a psychedelic, a few days, weeks, or months after a trip, a "flashback" can occur.
ive heard LOTS of reports saying how flashbacks are induced or intensified by smoking a simple bowl of MJ.
ever heard how psychedelics change someone forever (positive or negative) after their first use?
this and flashbacks kind of fall in the same category.
ive noticed (me personally) that the more LSD i do in a short amount of time (lets say i drop L 5 times in 3 months)
that i get heavier and stronger flashbacks.
but after a few days, weeks, months or even years (depending who you are) these effects will diminish (unless you decide to trip again)
