I imagine it's different for everyone. I posted a pic in your other thread of how I see the world, that is to say, blurry, surreal and as if everything is swaying a little, but that's just my own vision-based perception. Others experience tunnel vision, visual snow, a 2D world, or a world that looks as if it is behind a pane of (frosted) glass. For others still, this condition is indeed only a feeling, which is more the depersonalization aspect - the abject loneliness, existential dread, feeling disconnected from mind and body, and relentless anxiety. Some people experience both. So it's kind of an open-ended question, and probably needs a little more refinement if you want better answers.