Depression, whether an independent diagnosis and exacerbated by endo or as a by-product of endo, is prevalent in endo patients:
"This cross-sectional prospective study evaluated 100 women receiving care at the Outpatients' Clinic for Endometriosis, Department of Obstetrics and Gynecology, Universidade Estadual de Campinas (UNICAMP), Campinas, São Paulo, Brazil, equally divided into two groups: one suffering from chronic pelvic pain and the other pain-free. The Beck Depression Inventory was used in order to measure depression.
RESULTS:
Depression was detected in 86 and 38% of the women with and without chronic pelvic pain, respectively. Complaints of depression, such as somatic concerns, work inhibition, dissatisfaction, and sadness, were observed at a significantly higher rate in the group with pain. A sensation of failure was the only variable observed more frequently in the pain-free group.
CONCLUSIONS:
Depression is highly prevalent in women with endometriosis, especially those with pelvic pain. Careful evaluation can identify women with depression who may benefit from treatment." http://www.ncbi.nlm.nih.gov/pubmed/16521687
It an be further compounded by the use of hormones as treatment, as some hormonal suppressants can cause depression: "The brain in women has been shown to be an estrogen target organ. Common symptoms are shared by women complaining of PMS, postpartum blues, the perimenopausal transition and menopause: depression, sleep disturbance, irritability, anxiety and panic, memory and cognitive dysfunction and a decreased sense of well-being. The antiestrogens progesterone, progestin and tamoxifen may also elicit these same symptoms. It is proposed that whenever brain estrogen levels fall below the minimum brain estrogen requirement, for whatever reason and at whatever age, brain center dysfunction may ensue." http://europepmc.org/abstract/MED/8887186
Also it is well shown that endometriosis can cause chronic inflammation: "In response to a peripheral infection, innate immune cells produce pro-inflammatory cytokines that act on the brain to cause sickness behaviour. When activation of the peripheral immune system continues unabated, such as during systemic infections, cancer or autoimmune diseases, the ensuing immune signalling to the brain can lead to an exacerbation of sickness and the development of symptoms of depression in vulnerable individuals. These phenomena might account for the increased prevalence of clinical depression in physically ill people. Inflammation is therefore an important biological event that might increase the risk of major depressive episodes, much like the more traditional psychosocial factors." http://www.nature.com/nrn/journal/v9/n1/abs/nrn2297.html