In that state, where you don't know that information is missing, or that something is hidden, you believe that you're seeing the whole truth. You therefore make sense of it, and it seems to be what it is, based on its appearance. You think you're seeing the truth because you think you are seeing fully.
But if you are not seeing the whole of the information, and some information is hidden, you aren't seeing the real truth. So when you then believe that you are, you're inside a hallucination.
In other words, you're seeing meaning where there is none, you're convinced you're awake but you're not, you're certain you are making complete sane sense out of what's happening but you're mistaken, and you don't even realize that you're nuts.
This state of insanity is automatically a state of imagining truth where there is none - a hallucination of the truth, which is a state of believing the truth is something it is not.
Puzzles are another good example. When you first encounter a new puzzle, you do not see the answer. It seems obscure, hidden. At first you are confused, and you don't understand it, and it makes no sense, and you can't "see" how it is possible. And yet it seems to be possible that the unsolved state of the puzzle is truth, because you see no way to solve it or see additional truth beyond that. But over time, as you question your perception, you gradually might realize that by undoing your own assumptions and reversing your own conclusions, i.e. collapsing the hallucination, the answer suddenly becomes obvious.
Once you have solved the puzzle, it's because you've seen some information, really a state of greater awareness, which has burst the illusion and suddenly you are seeing outside of it. You are no longer fooled, you've found the answer, it seems clear as day and now you kick yourself for the apparent stupidity of having not seen it earlier. In other words, you realize you were mistaken the whole time and its pretty embarrassing.
Bringing this around to A Course in Miracles, it is the same with the "illusion" that this world is a reality. There is an illusion here, in front of your face, which if you were able to see ALL of it clearly, you'd see past the hallucinations and the misinterpretations and the misunderstandings, and suddenly realize, in a state of greater awareness, that what you THOUGHT was true before, was actually false. And you'll understand why. Because now you have revealed some kind of awareness of information that was hidden before, and this information is vital to being able to see the illusion correctly. Ie to overlook the deception, to overlook the delusion and insanity, which was telling you that all kinds of other stuff was true.
So right now, unless you're in full awareness, you're still inside what seems to be a puzzle. And because there's some stuff you are blocking from awareness, there's some information you are not privy to. And because of that limitation, and because you don't even know that the extra information exists yet, you believe that you're seeing the entire truth as it appears to you. That's in spite of the fact that you're only seeing part of a scene, are coming to false conclusions, are seeing "truths" which actually aren't quite true, and are therefore having hallucinations about the meaning of what you see.
You see a dark shadow behind a door, and because you lack information - awareness of "God facts" - in your belief that you are seeing correctly you believe that "its true" that there is a scary monster behind the door. However, if you turn on the light, which reveals to your awareness extra information, now it becomes obvious it was just clothing, and you once again kick yourself for falling for the silly belief that there was a real monster there. But before that, you really believed there was a real monster, and you were therefore frightened. Frightened by an hallucination - a false belief about the truth.
When there is enough awareness of "what is here", of what this illusion IS, its structure and purpose and functioning, and the ways that it deceives, it is no longer possible to believe the magic trick. You've seen through and past all of the mistaken perceptions which you thought were showing you reality.
All of the horrifying mis-truths that you believed in, such as that sin and death were real, are revealed to be completely false. All of the reasons you ever had to be afraid, suddenly have no foundation whatsoever because the truth emerges and shows you that the things you thought were frightening were not TRUE, they were delusions and hallucinated meanings, and thankfully there is a larger explanation for them. When you don't understand what is happening or why its happening, it will scare you, because the illusory truth it presents makes it seem real. When a correct explanation is given, you're like, oh... okay then. Then you drop the false belief, with relief that you no longer have a valid reason to be afraid.
So a blockage placed on awareness leads you to believing that the meaning of reality is obscured, the truth no longer quite makes sense but still seems true, you see things IN and ON TOP OF the illusion that are not even really there (thereby hallucinating), and the sense that you make of it is actually a deception. When the blockage to awareness is lifted, you can no longer be deceived. It's like hearing the punchline to the joke, and never again can you hear the joke and have quite as much of a laugh because you know the answer. Knowing the real answer, the real truth, is revealed by awareness.
So here's a question. If there is a grand illusion of a physical universe, a world, and a body, and if the only reason that you believe you're even seeing them is because you are lacking awareness, then doesn't it suggest that if you had enough awareness, you might suddenly see past that illusion and realize the world does not even really exist? It was just a kind of twisting of consciousness, a distortion, which you could only experience while insane and hallucinating? Maybe the world you thought existed was your misinterpretation of reality, and only existed as a hallucination based on a lack of awareness. Maybe there is no world.
Jesus said in relation to seeing through illusions, "What is understood as nothing must disappear."
"My body disappeared because I had no illusion about it. "!!
It's not just that there really is an illusion. It's only even an illusion because you believe there is one. Really, you are just misperceiving reality. That misperception shows you an illusion that there is a world. Once the puzzle is seen through and the truth is revealed, you will no longer be able to perceive that there really is a world. You will not believe it. You will recognize it was just an illusion, and nothing about it was ever really true. Like a dream. Not a real dream, but a dream-dream.
Form, matter, bodies, the universe, events, people, places, sins, guilts, death, sickness, it's all an illusion, a deception that APPEARS TO MAKE SENSE or appears to be real and true, ONLY because we lack awareness, and ONLY be cause there is some hidden information. When all is revealed, all of these illusions must disappear into the perfect omnipresent light of God, in which they DO NOT EXIST.
In reality, the world does not exist. We're dreaming it, hallucinating it, imagining it, reading into it, and are TRYING to make it a reality. It's just what you get when you haven't solved the puzzle yet, because the truth is obscured. When the truth is revealed, it will be obvious that there isn't really a world there. It was part of the puzzle while you fell for it. And now that the light has come, it is gone.
Lesson 75, "The light has come":
"The light has come. You are healed and you can heal. The light has come. You are saved and you can save. You are at peace, and you bring peace with you wherever you go. Darkness and turmoil and death have disappeared. The light has come. Today we celebrate the happy ending to your long dream of disaster. There are no dark dreams now. The light has come. Today the time of light begins for you and everyone. " - ACIM