I'm convinced that my wife is living with undiagnosed BDP.  Her behaviors match many of the experiences recounted here.

What I have noticed, however, is that morning-noon-ish, she's almost normal/nice.  It's only as the day goes on, she gets worse and worse... by evening, she's angry, nasty, belligerent, argumentative.

It's almost like 'sundowning' experienced by Alzheimer sufferers.

(I'm guessing it's just her ability to control her emotions drop as she gets tired, hungry, fatigued, etc... but what the hell do I know, I'm just guessing)