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I would suggest that before ECT, you look into TMS - trans cranial magnetic stimulation. It is supposed to be as effective as ECT w/o the side effects of it.
TMS for severe depression - Effective non-invasive treatment
Other things to look into would be (if you're open to it), consulting with a naturopath. Depression had been linked to inflammation and diet. Inflammation and depression correlation had been studied; one study had been conducted at Emory University in Atlanta, GA.
If you have not had a sleep study, it is also a good idea to look into it.
The link between sleep and depression: the effects of antidepressants on EEG sleep