As you can see from your Wikipedia article, you are certainly not the first person to get mired in these thoughts. How do you know that you’re not a brain in a vat? How do you know that we’re not all residents of the Matrix? Every generation comes up with a new version of the same idea. It’s like walking a labyrinth. It’s a puzzle that you’re not necessarily meant to solve, but the walk itself IS the solution, if that makes any sense. There are times in meditation that I feel “as one” with the universe and it all makes sense. It’s a wonderful feeling while it lasts. But then… whoosh… it’s gone again.