Paranoid Schizophrenia vs. Delusional Disorder in "Shutter Island"

I just watched "Shutter Island" for the second time last night and I got even more out of it than the first time.  Lines like, "you don't choose to be sane," really stand out.  If you haven't seen the movie I don't want to spoil anything here, so suffice it to say that it takes place at a high-security facility for the criminally insane.

I was reading about the film online this morning and learned that there is some debate whether one of the characters is actually schizophrenic or has what is called "delusional disorder,"  In both cases, a person can be high-functioning.  So what's the difference?  I'll try to simplify what's in the DSM-IV (the official book of psychiatric diagnosis).  Delusional Disorder is less serious than Schizophrenia.  Generally, the individual affected does not hallucinate and has delusions that are closer to a kind of paranoia about real things going on. In the case of schizophrenia, the individual affected does have hallucinations and usually has more fantastical delusions like about aliens, or insects in their brain, for example.

I was curious about the difference because I related to a character who had a highly delusional complex, but was still high-functioning, as I had been until I bottomed out about 5 years ago.  I was hallucinating hard, though, and the grey aliens and government spies watching me were all part of my psychosis, and this had gone on for years, so I definitely fit the schizophrenic category.

My point here though, (besides that you should see "Shutter Island" if you haven't already) is that these two illnesses can mimic each other without proper diagnosis and can go un-checked in higher functioning individuals.  If you or someone you know may fall into one of these categories, consult a doctor for proper diagnosis and treatment.