Netherworld Crazy Nightmare

"It's fake, it's all fake, don't be fooled, don't be fooled!" "Don't go, it's all fake. If you go, you'll never come back!" "She lied to you. Just go through this door and everything will be fine." Real or fake, sometimes it's not so clear. If the world can be fabricated and memories can be modified, how can we be sure that we are still ourselves?