Yep gobal, I mentioned it because I knew it would be an example that many could relate to. (DJ w/ 8 hands)
I guess the thing I want to say is that if we are to make some progress in understanding (or trying to understand) these visual phenomena, then we should improve our language (by naming things that show particularities).
To be honest, those videos about swirling lines and dots that try to represent the "LSD" visuals (not the experience) fall short. At least, haha, I think that an aquarium or snorkeling or the heat of a desert highway is nearer to LSD visuals than those Youtube videos. But anyway...
Terence McKenna insisted that we should improve our language and be clear about the terms etc, and yet, he made a big mistake calling his book "True Hallucinations". Because Mushrooms and DMT do NOT produce False Hallucinations or True Hallucinations. They produce Visions.
Are Visions real or imaginary? That's the debate that been going on here. That what OP wants to find out.
Are illusions real? Well, an illusion is a distortion. An alteration of a shape. But the original and "real" shape is there... but the observer thinks the shape has different characteristics, being the cause an altered perception (LSD, TCH) or an optical illusion (3 Fingers, Crossed Eyes).
Are Hallucinations real? Well, a hallucination is a perception in the absence of a stimulus. KEY-FUCKING-WORD: Absence.
Schizophrenics sometimes tell that there is a person there that is trying to hurt them... but I don't see it. There is not even a regular person there. They are "creating" that imaginary "person"(visual hallucination). Sometimes they hear voices when there is absolute silence (auditory hallucination). Sometimes they feel insects inside their skin when they are just sitting there in the benches (kinesthetic hallucinations). They imagine things without any stimulus and they are not seeing mandalas. They are having Open Eyed Hallucinations.
Which drugs can create Hallucinations? Datura and other tropane alkaloids. Probably others too, I don't know. But the thing is that both on schizophrenia and Datura intoxication the person under a state of delirium. That means, the person thinks that what he sees is real because it SEEMS real. It is on this world, the people they see have regular clothes, the animals they see have an anatomy that is based on the anatomy of "normal" animals. Sometimes they see giant spiders... but the spiders look like "normal" giant spiders. They don't look like like something indescribable. So, are hallucinations real? I don't know... it's complex. I guess they are not "real", but of course, I don't know the nature of reality and therefore I couldn't say.
I mean, what IF it turns out spirits are real and a schizophrenic patient says he/she sees spirits? What is one supposed to do?
Now... Visions are real or imaginary?
Well, you are altering your perception with a drug. But that doesn't mean the visions are not real. After all, if you study psycho-pharmacology you'll see that our brain perceives thanks to certain drugs. Except that those drugs aka neurotransmitters are endogenous. So... in my opinion it is VERY (and I mean VERY) possible that the particular visions DMT produces may be real. Because, in a sense, what the DMT could be doing is that is expanding your perception so that the brain can receive more signals, like if the brain was some kind of antenna. [Add more theories here]
So in short, my opinion is:
Are illusions real? Of course they're not.
Are hallucinations real? I guess they're not.
Are visions real? I guess they are.