Endometriosis, is a condition where tissue from the uterus, called endometrium, grows outside of the uterus. This effects up to 10% of women, and can lead to long-lasting, moderate to severe pelvic pain, infertility and other symptoms. This can affect a woman's quality of life (including increased risk of depression and anxiety) and is associated with increased healthcare costs. Current treatments are often limited by serious side effects, and many women resort to surgery. Surgery is also associated with complications and there are long wait times for procedures, sometimes over 3 years. This means that many women continue to suffer from symptoms while they wait for surgery. Therefore, new effective treatments for endometriosis pain are needed. New research suggests that inflammation and stress caused by lack of oxygen in the affected areas may cause endometriosis. Hyperbaric Oxygen Therapy (HBOT), where patients are placed in a small chamber with higher than normal levels of oxygen, suppresses inflammation and promotes tissue healing. Because inflammation is central to this condition, HBOT has emerged as a potential treatment. In this study, the investigators will test if HBOT, in addition to the standard treatments, is more effective at treating endometriosis pain than the standard treatments alone.