Season 2 finale question (spoilers obv)

Great episode, but left me confused. For pretty much the entire episode, the audience is led to believe that House was shot in the stomach and neck and he had some sort of ketamine treatment that healed his leg but messed with his mind. Hallucinations in TV shows always fuck with me. He has conversations with the guy who shot him, but some of them turned out to be halluconations? Was any of that real? We see that House kills the patient on the surgery table. Pretty sure that wasn't real, but I'm not positive. After that, it cuts to a scene where House is being rushed for treatment after being shot. He says "tell cuddy to give me the ketamine" or something along those lines. I don't know what was real and what wasn't. I'm not very comprehensive of television plot twists. Can anyone clear this up for me? Please no spoilers, I haven't started season 3 yet. Thanks in advance.