Extended Answers (spoilers contained within)
Seems like this is a direct take of the Tell Tale Heart,....
Man kills wife,.... wife "haunts" him,.... he goes mad,...
Here what I think,...
1. The Police - were REAL, not imagined. Only ONE part in the movie has "imagined" police,... the late night phone call(which eventualy traps HIM in the lie)
2. The Gym Teaching Lover - was also REAL. So was the beating, so was the baseball bat and broken front door.
3. The Psychologist - I say was REAL. He gave the pills that were supposed to help him "sleep", when in my opinion, they acted like Sodium Pentathol, which is commonly known as "Truth Serum". Any one that knows about law enforcement know well what true truth serum does. It does NOT make you become honest.... it basicaly DRUGS you to the point where you feel so groggy that you dont realize your telling them everything. That is why they STOPPED using "truth serum", because Judges were throwing cases out over the whole forceful drugging for information thing. Kinda like entrapment.
4. The Baby, The Ghost, and The Finger - I believe the word is DELLUSION, not ILLUSION as stated by others,... since it was NOT "set-up" like a magic trick, it was HIM just goin nuts,... dellusion.
5. The Pipes - OLD PIPES = LEAKS, SOUNDS, FLOODING, and WATER DAMAGE,... any plumber or homeowner knows that.
6. The Ghostly Assault - Hello, Im reality,... welcome me, people. She had MEDICATION in her bag! Inhalers are NOT ALWAYS for asthma, they can be used for MANY types of direct medication. She even SAID that she felt dizzy and passed out. She was most likely epileptic or something, which would be why she hit the floor like that. PLUS, She said she HEARD a woman scream, and she herself was bleeding from her FACE. I would think she would have pointed out seeing, or at least feeling some thing hit her face? Of course! The reason she was bleeding, was because she dropped and busted her nose open on the floor. Hence the blood only being on her shirt.
7. The Neighborly Disturbance - Get with it folks!!! In one of the last scenes of the movie he HEARS his neighbors fighting, and then he hears the Man kill the wide(symbolized by the sreaming of HELP!!). DIRECTLY AFTER this, He looks out the window towards his neighbors house. He sees the man open the window and look around, as if he was seeing if any one heard what happened. If you look closely, youll see the neighbor in the window is in fact HIMSELF.
8. The Phone Call - Ok, this is a recap of the mentioned phone call,.. there are clues when he takes his pills. He drinks alchohol despite the warnings of Sadie, who even tells him it'll make the meds absorb in to the blood more rapidly. In other words, the phone call was a dellusion, caused by the meds retro-absorbing into the bloodstream before he actualy fell asleep. He then "confessed" to himself, by "dreaming" while awake, that he killed his wife and buried her in the woods. The next day, the doctor comes to visit, and keeps asking about calling the police. He kept pushing to call the police, over and over,... this is a form of psychology. When he finaly spoke, he said they called and had told him she was buried in the woods. THEY HAD NOT spoken to him AT ALL. Thats where he traped himself.