What causes irritability, nausea, waves of hot flashes, and lightheadedness before onset of menstrual cycle?

Pieces of PMS: The coming and going and variation of amounts of hormones can have impacts in all sorts of body systems - especially in some. Also, some are more aware of and sensitive to the feelings. When you think about it, the process of preparation for, duration of and elimination of fertility is a pretty big deal. It's the "miracle" of life! (even if you are not pregnant).