You can't fathom existing nowhere. Doesn't that mean that you are everything around you and not just what's on the "inside" ?
No. It means that
everything that you perceive to be around you is an incomplete picture created
within you. It means you can only
perceive the experiential qualia that spontaneously bubble into your conscious awareness.
Actually wait - let me correct myself. There are different ways of looking at the situation. Also -
yes, you are everything around you, because the things around you all originate from subconscious processes that are, in actual fact, still "inside" yourself.
You cannot actually
directly perceive
anything outside yourself. It's quite possible
there is nothing outside yourself, for you have no way of truly, objectively verifying that your perceptions are anything other than a part of yourself.
It's up to you what you choose to infer from this. Most people find it easier to navigate this strange internal space if they assume that the
representations of things "outside" their minds actually
do represent something "real", passed through the filters of our sense organs, followed by the computational decoding that occurs in our cognitive organ (the brain) to result in a fairly neatly packaged simulation of a reality outside our minds that has it's own existence. But there is no way to truly verify this. Our entire biological paradigm of neurological processes, different brain structures, sense organs, the reality we infer to be exist outside ourselves, are based on things that we just have no way to
directly perceive,
without filtering them through these lenses that might be themselves complete fabrications originating from a place within our minds but outside our conscious awareness.
Equally, most people find it easier to navigate existing within an apparently conscious mind, inside something called a "human", if they assume that the
other humans they perceive seem to also have their own internal experiential worlds, even if not exactly the same ones as your own, and not ones that you can ever directly peek into, even if they are complete fabrications created by your own mind and in fact, you are the only truly conscious, sentient entity in all of existence.
But neither of these perspectives are compulsory. Either
could be "true".
As far as you can tell, really, you are the only sentient entity in the entire universe. In fact, you
are the entire universe, and other people's lives are not actually happening, but just stories that seem real only when they intersect with your own. I - or, probably, most of the representations of other humans that you meet - can tell you that I too have an internal world, it's not just you - in which case, there must be some reality "without", and this points to the existence of a greater reality that the low-resolution simulation your mind constructs for you as some kind of workable, if incomplete, model.
But then, we would all say the same thing if we were nothing but convincing illusions created from a place within your own mind.
There's really no way to tell for sure.