other than the fact that her name was created in his head by the brand of one of his wife's sweaters.
When he asked her if she wanted a drink she said you shouldnt mix wine with medication. How did she know he was going to pull wine out of the fridge? Because she's in his head.
Is it possible that all the characters who were popping pills weren't real?
That maybe he was hallucinating them all, like he had dissociative disorder at that point and those other characters were his other personalities (hence they were popping pills just as he was?)
11/16/12: The day the Twinkie died :(
I had just rewatched this movie recently, but I don't think there is any MPD going on here. What I think is happening is that most of the film is a confused mismash of remembered dreams and erroneous recollection of the events after his wife's death. Daniels character complains he never sleeps, yet almost every scene features him waking up. He is clearly sleeping quite a lot according to the viewer. So what is going on here? Why is he having so much trouble staying awake? He complains about insomnia but dreads sleep.
Theory: Daniels 'awake'/'lost-time sleep' cycle is actually him coming in and out of a comatose->brain death state after swallowing the pills at the end of the film.
When Daniels is 'awake' he is actually suffering nightmare delusions about murdering his wife as he lays unconscious. When Daniels loses time before 'awaking' again, he is possibly arresting or suffocating before coming back to his comatose state and somewhere further in his disjointed dream remembrance of the events that led him there colored by his subconscious knowledge that HE DID murder his wife and all the guilt that comes with it, and the conscious need to deny this information which lead him to swallow the pills in the first place.
The pill popping never makes sense by any of the characters, it's likely Daniels finger-wagging subconscious is recalling the pills as well as Daniels conscious mind searching for his 'sleep' solution. More pills!
So, simply, it's an unreliable narrative told by a character overdosing on sleeping pills. He was guilt ridden after (possibly) murdering his wife and couldn't sleep, or stress and the disappearance of his wife led to a breakdown where he believed he had murdered his wife (who may have just run off with the gym teacher (who may himself just represent some 'jock' that stole his wife)). The stress led to insomnia and depression and he eventually swallowed a bottle to kill himself. Ironically the sleeping pills aren't curing his insomnia, they are now the thing keeping him 'awake' as he lays in a drug induced OD coma on the floor(causing the lucid dreams and bringing suppressed aspects of his psyche to surface. The very things he didn't want to face in the first place!)
The whole thing is circular and revolves around the pills. He has insomnia and can't sleep. He takes pills to make him sleep. Pills cause him to have bad dreams. Bad dreams cause insomnia. He eventually takes a bunch of pills to kill himself, but taking a bunch of pills to kill yourself causes really wacky lucid dreams wherein he remembers he has insomnia (where audience comes in). He remember he needs to take pills to 'sleep'. But in this case the pills he needs to 'sleep' are actually the pills he needs to kill himself.