If I accidentally get "Left Behind" at the Rapture, what will happen to me?

You can't be "accidently" left behind. God makes no mistakes. Only you can, which is obviously the reason you would still be there. You would expect to feel no connection to God, because he would withdraw his spirit from the world. Therefore you will go through the tribulation. So while you have the chance, you better repent. You don't want to be left behind.