Deep endometriosis: What are the causes?

I've been having weird symptoms lately such as blood in my urine, horrible pain in the pelvic zone and in the lower side of my back. I came across an article about deep endometriosis and it seems to match my symptoms.

I have an appointment in 3 weeks with my gynecologist but I'd like to know if any of you know what this is and what is are the causes.

Thanks in advance.