Menorrhagia is the medical term for menstrual periods with abnormally heavy or prolonged bleeding. Although heavy menstrual bleeding is a common concern, most women don't experience blood loss severe enough to be defined as menorrhagia.
With menorrhagia, you can't maintain your usual activities when you have your period because you have so much blood loss and cramping. If you dread your period because you have such heavy menstrual bleeding, talk with your doctor. There are many effective treatments for menorrhagia.