Endometriosis is a chronic, painful, debilitating, frustrating, enervating disease. Most people have never heard of it, a lot of people cannot pronounce it, yet it affects 10% of women. It is extremely likely that you know someone with endometriosis, even if you don't know they suffer.
It is often dismissed as "women's troubles", and the funding to deal with endo on the NHS has been slashed. But it is the highest cause of infertility and the second most common gynaecological condition. It can be isolating and soul destroying.