Heavy or prolonged menstrual periods, or menorrhagia, is the most common type of abnormal bleeding from the uterus. Heavy period include nighttime bleeding, passing large blood clots during menstruation and a period that lasts longer than seven days.
It could be due to hormonal imbalance, Fibroids, miscarriage, blood thinners, birth control, cervical cancer or thyroid. There are good medications to treat these conditions.