The "schizophrenic" explanation to the preceding events may be becoming more popular these days, but as films like Haute Tension have shown us this can still be a very effective and unpredictable move.
Similar revelations in Fight Club and American Psycho work well (just don't read the books first! er... or this post :p)
I'm more concerned about the "they're really dead!" theme, since The Sixth Sense was glaringly bloody obvious (main reason: Bruce Willis in the title role - his presence reeked of something afoot right from the start that the director desperately tried to conceal until the end) - though The Others wasn't so!
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