It is thought to be related to changes in chemicals in the body called hormones. About half of all women have PMS at some time. It becomes more common with age. We do not know why some women have more severe cases than others. Stress seems to encourage the problem.
Many different changes can occur.
Most women have only a few. Some women have trouble with thinking or concentration. You may feel very tired or have trouble sleeping. Some women feel dizzy or may faint. You may have changes in your bowels such as constipation or diarrhea.