Vodsel, good points, specially about how just because we naturally see patterns doesnt mean that 'objective' patterns aren't there at least some of the times

As for "quantum entanglement", I dont know enough about quantum physics to really use that in an argument, I would just be using some words very superficially if I was to debate that aspect... But nevertheless I think your main point stands, that we dont know enough (yet?) to be able to affirm something with absolute certainty at this point.
Hyperspace Fool, interesting post! I think its a very good point about how one could "chase the rabbit" of a seeming synchronicity and see where it leads, as it might lead to somewhere interesting, as it did many times in my life (though no free diving trip yet!

). But of course, as you are well aware and we talked before, a balance is always necessary. I can see how some people could for example become obsessed and paranoid about one or another theme from some synchronicity they experienced, and could lose track of other things in life and instead of 'seeing where the rabit hole goes', actually be digging their own direction-less hole that they cant get out of. So where do we draw the line? I guess its very contextual, and it depends on each person and how they are in life and what are the other responsibilities that one must fullfil. Thats why I think questioning oneself continually is the way to go... "Am I overdoing this? Are there more important things I should or could be devoting energy to at this moment? Is this search for the meaning or direction of the synchronicity having a negative impact on my or someone else's life ? etc".
By the way HF, I would love it if you shared some of your hypothesis regarding synchronicities, even if they are very far out. I love thinking far out, when we are aware they are hypothesis that might not be true (or might be... but we dont know it, at least yet).
DoctorMantus, I think you are totally free to have your own beliefs when, as you express, you are conscious they are beliefs, and if they dont hurt anybody. Nevertheless, personally I see it as problematic (for myself, if I was to follow that) to fall into a belief that there are no such things as coincidences first of all because as citta and others mentioned, there IS such a well-explained phenomenon as perceptive filtering/apophenia, and it's easily explained by how it has offered some evolutionary advantage to humans (But of course, to say that all synchronicities are simply that is, as mentioned before, purely speculation). But also because it could lead to some paranoid/obsessive thinking. In psychiatric jargon sometimes they talk about 'self-reference delirium' for some psychosis, like when you scratched your ear because you had it itching, and a schizophrenic paranoid delusional person might think you are sending signals to the cops to arrest him/her, or whatever. So in the same lines as ragabr was asking, how does that make it when you are a part of someone else's "synchronicity"? If we take that thought to the extreme, can you see how this would lead to a lot of contradictions?
Citta, thanks for the elaboration! I still find a few issues with your thinking that I think we can discuss a bit... I understand that believing the effects of DMT are hallucinations do not necessarily make the experience meaningless or without value. In fact, even if we could prove somehow that it was "merely" hallucinations, I still think there is great value in it. But thats not really my point, the fact is, that it is still a belief that has no data to support it, and just like I said to doctor mantus, I think its fine if you are conscious its a belief and it hurts nobody, but do know its a belief and not a fact, and not necessarily more likely than any other belief (just like supposing all synchronicities are just 'empty' coincidences)
You say that tests can confirm that certain stimulations can induce certain types of state, again while this is of course interesting, it is no evidence at all of a causal relationship, that is merely a supposition. Maybe you dont personally think that the TV analogy is true, but that is your own personal hypothesis, speculation or belief. Sure, the 5HT2a is directly connected to the experience (for example how ketanserin blocks psychedelic effects by being a 5HT2a antagonist), but this only shows how 5HT2a is the pathway through which the activation that leads to the effects happens, but it does not in any moment tell us that the effects themselves and all the phenomenological experience is created by the brain or by the 5ht2a receptors.
And as for your question of the computer screen, arent you using an analogy that contradicts yourself? You are saying that a new code changes what the screen presents, but the data from what is appearing in the screen is NOT created by the new code or by the video card, the data is being created elsewhere (in the harddisk), and the videocard and new code is merely modulating the image
and I would disagree with you here. From a critical perspective, there is no reason to assume the image is being created by the new code or the video card, just like there is no reason to assume the dmt experience is created by the brain or the dmt molecule, all we know is they are modulated by it, that there is a relationship, but we dont know that its a causal relationship (we neither know that its NOT a causal relationship, but there is no reason to assume either way, from a critical perspective). In the same way, from a critical perspective, I think there is no reason to assume all synchronicities are just coincidences, just like there is no reason to assume that all coincidences are meaningful synchronicities. Both are just speculation.
With that being said, so what is the use, in practical terms, of not assuming either way? What is the difference, why does it matter?
It matters, imo, in the same way that it would have mattered to NOT suppose the sun revolves around the earth, even though in practical terms at the moment, for all people cared at the time, supposing the sun revolved around the earth made perfect sense according to data people had, and people could still live a meaningful life. But if you assume one way, if you believe one way, you are closing yourself from considering an alternative that might be true, no matter how unlikely. If you assume that all of hyperspace is just brain perturbation or that all synchronicities are just coincidences, you might be closing yourself from devising experiments and exploring the world in a way that might result in a breakthrough in understanding, that might lead to new knowledge, that might have practical benefits, just like finding out about heliocentrism ended up having very practical consequences even if before it didnt matter, or if the other assumption worked well enough for the moment to explain the phenomena at hand. Of course, as I mentioned before, contemplating the different possibilities, even the unlikely ones, requires a limit, requires critical thinking, because we have a limited time, and there are unlimited alternative possibilities to explain all phenomena, so we have to somehow limit ourselves to what we think might be beneficial, to what possibilities might have some worth contemplating or investigating, and to what extent taking that investigation. But then wouldnt it be much more critical and interesting to consider where could be the guideliness of that alternative exploration, to consider what questions can be asked and how could they possibly be answered in a way that doesnt inhibit 'normal functioning', instead of assuming one thing with pretension of Objectivity while in fact its just a belief like any other belief, even if it seems for the moment the most likely (even though thats arguable)?