Crazy and mentally ill are much the same thing; what separates the crazy from others suffering from normal mental health issues is the extremity of their behaviour. Take 'Fatal Attraction' as an example. Glenn Close's character had obvious self esteem and relationship issues from the get go. She's portrayed as a man eater who overcompensates with her animalistic love making. She's insecure and a tad on the obsessive side. Michael Douglas uses her when we see he has a perfectly good wife at home. He's rather abrupt when he calls off the affair and this exacerbates Close's personality and depressive traits. She is in love and obsessed with him; all he wanted was a bit of wham bam thank you ma'am. She goes into extremely jealous and vengeful psychosis and attempts to wreak havoc on Douglas and co. Bunny boiling, child abduction, house invasion, hell hath no fury. So to answer your question old Glenn Close was a depressive with borderline personality disorder at the start of the movie. These traits were masked and therefore suggest a split depressive personality. Rather like a land mine, Douglas' rejection triggered the fuse which revealed the latent psychotic sociopath, or, to put it lightly, a 'crazy' deranged woman.
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