In the following I consider "reality" to be "all the sensorial evidence a living being can obtain by interacting with its surrounding world".
I am setting up a world where two realities exist, but they are mutually orthogonal. To clarify this concept, look at the image:
The thing A, projected on reality Y is different from a dot, therefore it exist in that reality and can interact with it. In reality X instead its projection is a point, meaning it cannot interact in any way with that reality and its entities. To make a long story short, reality X is non existent for A.
The thing B has the same, but with reversed outcome.
The thing C is a very rare case (1 in a billion or so) of something that can interact with both realities.
Now my question is: if A, B and C are sentient creatures, is there any way that C can prove the universe is structured in this way, or will he always be treated as a lunatic from both A and B? (The universe is not limited to the only A, B and C)
For the sake of clarity, reality X and Y are not geometrical directions. You may name them as "physical world" and "spiritual world" if it makes easier to grasp what I mean.