Why do women get all emotional when it's THAT ...

There are several explanations as to why women get mood swings before and during menstruation. According to "Women's Health Information" it relates to the balance between estrogen and progesterone, you can find more information here:

http://www.fwhc.org/health/moon.htm

As I experienced from my girlfriend, during menstruation women are more likely feels anxiety that caused them to get emotional at all times, they need time to rest, and for as for men, they need to get patient in times like that to avoid conflicts specially when women is suffering from menstrual disorders .

As Ruth says it's to do with hormones. It's just the way they are and something you just have to accept.

Women find us just as confusing the way we're so overly competitive, aggressive and unemotional at times and this is because of the hormone testosterone. Unfortunately we aren't allowed to use it as an excuse for our behavior the way women sometimes do!