Don, there are Ketamine trials that are, apparently having good success with resistant and severe forms of depression. I was very distressed to read your other comment, which may or may not have been approved (it came up for me to rate). If you have nothing to lose, perhaps try something radical - take off indefinitely for an immersive volunteer experience abroad - with animals or nature, which are so healing. I just watched a doc called "I Am Not Your Guru" about a 5-day Tony Robins program called Date with Destiny that has apparently helped people with suicidal depression. A lengthy meditation and yoga retreat - perhaps at an ashram, which can offer a very supportive community. "Full Catastrophe Living" by Jon Kabat-Zin is a great book. Anyway, i don't doubt your ability to make a rationale decision about this, and as you say, who knows better than you.  But maybe there are some options outside the typical remedies offered that you have not yet tried? I wish you well, Don!