Bismillahir rahmaanir rahiim...
From Aisyah r.a, Prophet Muhammad saw said, "This is something that Allah has set for the granddaughter of Adam (women)."
Menstruation is the beginning of a new menstrual cycle in female body. The uterine lining is formed upon every menstrual cycle and needs to be expelled from the body when conception has not occurred. At the start of every menstrual cycle, the uterine lining and decomposed egg exits the cervix, into the vagina and out of the body. Menstrual flow is not only expelled by force of gravity, but also the contraction of the uterus which helps force decomposed waste/menstrual flow out the body and thus, may results in abdominal discomfort in menstruating women (cramps or `senggugut' in Bahasa).
Comes/not with menstruation are PMS or PMDD. PMS (Pre-Menstrual Syndrome) covers the physical or emotional disturbances in a female. Symptoms of PMS include depression, irritability, crying, oversensitivity, and mood swings, plus common physical conditions like insomnia, fatigue, aches, bloating, cramps, constipation and headaches. A more severe form of PMS is PMDD (Pre-Menstrual Dysphoric Disorder). Both PMS and PMDD affect a woman’s quality-of-life, however, certain nutrition consumptions, stress-levels and predisposed factors may make PMS/PMDD more severe from one woman to another.
Read more about this at: http://meninmenstruation.wordpress.com/2010/06/03/be-informed-know-the-difference-pms-and-periodmenstruation/
According to Imam Syafi’ie, Atha and Abu Thur; the shortest period of menstruation is 24 hours (a day) and the longest is 15 days. Menstruation is considered to fall under the “normal” range anywhere from 6 to 7 days. And so, if the menstruation comes less than 24 hours or more than 15 days, it is claimed as `sickness blood’ or istihadhah. Menstruating women are forbidden by Syara’ to do solah, tawaf, touching, carrying and reading Quran, stay in mosque, fasting, having physical intercourse with husband and to be divorced/get`talak’.
Go to this link for Fiqh questions on women menstruation (sorry, they are in Bahasa);
...and also this link about replacing (qadha') the solah:
***Did you know the one who discover deeply about women menstruation is a man@ Imam Al-Ghazali? He wrote a Kitab Ihya' Ulumuddin that discussed specifically about this.
~toward His love~