7 months ago
Last edited at 8:08AM on 9/7/2013
Because the body reaction called the "period" is almost the same reaction body gives to a disease. So the outcome is expected to be similar. If you have an infectious disease, immune system gets activated to remove the virus or bacteria. When you have your period, the same immune system cells gets activated to remove the uterine lining. The immune system reaction in one direction can cause weakness in other so that might be your reason.