Interesting thread.
I tend to side with hashush's thesis that this phenomenon is just selective memory. I probaby disagree with him/her philosophically on most everything else.
I do believe that there is a reality (I call it the Real) "out there," truly and completely independent from our minds. This Real has no structure, no meaning, and no significance; these concepts emerge only when us humyns start developing symbolic (linguistic) explanations for events or things in the Real.
From this perspective, there seem to be two interpretations of synchronicity. Either it is nonexistent, a placebo, an artifact of selective memory, or taking psychedelics somehow influences the Real to better match up with our symbolic expectations. Lacking compelling evidence for the latter, I default to the former, although I can imagine some personal experiences I have not had might be able to change that view, and willow's comment about quantum collapse is some interesting food for thought.
I think it's a fallacy to believe that our minds "are" the universe / reality simply because they assign it meaning. I also think that hashush is responding to a different, weaker argument than the one samadhi_smiles made. My interpretation was not so much the "Matrix/brain in a vat" thought experiment silliness, but a more philosophic claim: the external universe is a construct of Mind, and Mind is the only thing independently "real." Reality as an external structure does not exist, only our internal (i.e., mental) image of it.
I distinguish myself from that view with my ascription to the Lacanian notion of the Real. Reality as such does exist external to our minds; however, this external Real is devoid of symbolic meaning. From this external stimulus, our minds construct sense-making paradigms based on language that interpret that reality and give it meaning. Regarding synchronicity, the things we find 'coincidental' or meaningful are purely symbolic; there is no 'objective' method external to our constructed systems of meaning that defines what is and is not important or even similar. The consumption of a substance by an organism and the various 'meaningful' events that are imagined to occur 'in sync' are related only vis-a-vis one's own subjective web of related meanings, or perhaps intersubjective notions of psychedelic meaning. As a parting thought, I would be more amenable to the idea of synchronicity if it were framed as an intersubjective thing (i.e., something regarding the shared, social network of meaning surrounding, in this case, psychedelics... perhaps related to some notion of collective consciousness) rather than a trait exhibited by reality itself.