Endometriosis is a chronic condition in which tissue similar to the lining of the uterus grows outside the uterus — on the ovaries, fallopian tubes, and other pelvic structures. This tissue responds to hormonal changes, driving inflammation, pain, and sometimes scar tissue (adhesions).
It commonly causes severe period pain, chronic pelvic pain, pain with sex, and can affect fertility. Debilitating period pain is not "just normal." It is common yet often under-diagnosed, with long delays; diagnosis may involve imaging or laparoscopy. See endometriosis.