Your thoughts, feelings and experiences create who you are, therefore the two worlds (inside and outside) can only exist together. If your mind exists, then the world that created it must also exist. If the world that created your mind doesn't exist, then neither can your mind. Could your brain be being fed false information? Sure, it's possible that this is all fake, but you must then accept that if your outside world is fake then so is your inside world. You are only as real as the perceived environment that created you; no more no less.