The only explanation that doesn't lead to absurdity is that drugs corrupt your perception. They interfere with and frustrate the healthy and proper operation of the brain and in doing so distort perception.
If you're willing to accept that you can't really rank or judge modes of mental experience quantitatively on some kind of non-relative scale (which would require access to a "reality" outside yourself), then it shouldn't be too much of a leap to say messing with how it functions within tolerable bounds could be more of an optimization (or equal but just different) to your experience.
Attaching doubt to things "just because" isn't rational and cannot be resolved rationally precisely because such doubts are not rationally motivated. If I say to you "I doubt that you are here", for no reason other than some arbitrary skepticism about my perceptual faculties, then there is no way that that doubt can rationally be resolved. The very idea of hallucination presumes a normative perception. That we can know that we can misperceive or be subject to illusions itself presumes that we can tell the difference. Otherwise, we are just positing idle and detached possibilities while tacitly, and paradoxically, drawing on various convictions about the real.
I understand you're looking at it from a scientific point of view, but the discussion is not scientific. Consciousness is probably the hardest body of knowledge to integrate with science. Nobody knows where consciousness comes from. Nobody knows how to measure it.
I can tell you: "I'm conscious and aware", but there's no way I can prove to you I'm not a philosophical zombie(someone that acts like it's conscious, but isn't). Currently, there's no way to measure consciousness.
>By your own standards, I could ask how you know there's something called a brain, that it has something to do with perception, etc. Maybe you hallucinated the brain? Maybe it's just some weird belief you have? Maybe hallucinations aren't a thing? How do you know what other brains do or don't do differently? And why can't some of them be wrong?
I think you nailed it. I don't know whether there's a brain, or if there is something else, and this something else is hallucinating this reality where there is a brain, or maybe something else entirely. Sure, we can make scientific claims about stuff when analyzing the reality within the bounds of our perception, but if you try to go beyondg that, you're own your own.
You can't prove that to yourself either, because a zombie has the same thoughts as you. You can't differentiate even subjectively whether you're a zombie or not.
I think the phrase "I think, therefore I am" is the essence here. A philosophical zombie does not "think". It looks like they do, but it's just a deterministic result of neurochemichal events going on in a brain that lives in the dark. Something like a neural network for instance. They can exhibit thought-like behavior without experiencing anything(as far as we know).