Endometriosis is a poorly understood disease without known cure. Endometriosis involves the female reproductive system but may also spread to distant organs. This is agony every month and causes time off work that can't be justified to an employer. I have provided references to information regarding endometriosis: http://endometriosisfoundation.org/

https://www.endometriosis-uk.org/news/new-research-could-mean-better-treatment-endometriosis-37171