I'm in the midst of having it and already feel the difference. I managed to put the dishwasher on today without feeling it was some Herculean task.
I'm also having Ketamine infusions which have had a drastic impact on the suicidal thoughts. I don't think that is that common though. Might be worth asking if ADDs haven't worked thus far though?
My depression is definitively not situational or even what I'd describe as emotional. Life, objectively, is better than it ever has been. Loving family, good job, secure finances/home etc. No major stresses.
I do have endometriosis and the pain is a contributing factor. As is the "chemical menopause" treatment. But that's been the case for years and isn't a sufficient explanation.
I had a hellish background/childhood - but also years of talking therapies with a psych I love dearly and who has more or less adopted me, which did wonders.
My depression is more an emptiness and absolute lack of emotion/meaning - more than deep sadness or anything. I don't know if that impacts what kind of treatment is effective or not.
As for adverse effects - I usually struggle to remember what happened directly before and after. It makes me pretty tired for the rest of the day, but not unmanageable. I get a headache too, but nothing that doesn't go over with some co-codamol.
Hope this helps - or that you're already well on the way to recovery! Depression is beastly.