I'm gonna just jump right in here with my thoughts. I have many.
Amber, The Psyche
Hallucination Amber is a little creepier than the live version of Amber that we knew in season 4. But she is merely a representation of House's subconscious, that has been manifested due to his feelings of guilt. To me, it is obvious why this has happened:
1) House is the master of guilt suppression. He regularly does things that the average person would feel incredibly guilty about. But House shoves that away deep inside his brain. That isn't to say that he doesn't feel guilty; it just...
"House M.D.: Three Stories (#1.21)" (2005) Dr. Gregory House: I choose to believe that the white light people sometimes see, visions this patient saw, they're all just chemical reactions that take place when the brain shuts down Dr. Eric Foreman: You choose to believe that? Dr. Gregory House: There's no conclusive science. My choice has no practical relevance to my life, I choose the outcome I find more comforting Dr. Cameron: You find it more comforting to believe that this is it? Dr. Gregory House: I find it more comforting to believe that all this isn't simply a test.