Ketamine is known for its hellacious side effects (horrible hallucinations, disassociation, deep feelings of dread) immediately after it's been injected, but it can also raise depression for days/weeks and sometimes even months after a significant infusion. I think that's what led to your last horrible experience, not the ECT. Please do speak to your doctor about ect but NOT having ketamine again.
The other thing I would say is that my daughter's depression did not truly lift until after her ect and the right meds and weekly sessions with an experienced therapist, and a nutrition/vitamin and excersize program. Sometimes it takes a lot of pieces to finish the puzzle. Please don't give up yet.
Sending you healing thoughts