As its name suggest, premenstrual syndrome, or PMS, strikes before your period. It affects over 90 percent of women a week or two before their period.
The symptoms, both emotional and physical, vary, as does their severity. Some women can continue on with their daily lives through PMS, but others miss work or school because of the associated symptoms.
PMS most likely occurs because estrogen and progesterone levels drop off significantly after you ovulate if you aren’t pregnant. The sharp drop in those hormone levels impacts your body, most likely triggering PMS symptoms.