What Am I Riddles

Question: I'm small but big, i hide behind you but come out when you fall... What am I?

Question: I'm just a lot of nothing but I'm every were... what am I?

Question: I hide when you wake but upset you as you sleep... What am I?

Question: I sit on a bridge so you might see just how clear the world can be. What am I?

Question: I was crucified to keep murders out of the maze. What am I?