This is considered one of the typical phases of alzheimer's. My mom would get very argumentative in the evenings. If she had had a few brandies - she would really get mouthy. I believe it has something to do with the lack of daylight and the confusion it can cause. I have a great book that deals with each phase - but unfortunately, it's packed away until hell freezes over. I'll try to remember the title/author and post it asap.