Lifesaver. I might as well end there, as that's how I feel about it. However, I'll go into the pros and cons.
It was "discovered" in the 20th century as a cure for depression. It was found that epileptic patients who were depressed got better after having a seizure. Consequently, psychiatrists decided that if they could artificially produce a seizure, people who were depressed might get less depressed. A small current was passed through the brain, without anaesthetic initially, and a seizure would take place. Patients were strapped to beds so that they didn't hurt themselves during the treatment. There was a lot of evidence to support ECT, but no one understood why it worked - what it did to the brain and mood. Actually, no one understands it today either, but it has a long track record of success.
Nowadays, an anaesthetic is used - the lighter the better - and a muscle relaxant is given beforehand. When you wake up, you often have a headache and your memory is totally shot to bits. That recovers - mostly - but sometimes leaves you with a gap. Otherwise there are no side effects, or none that have been discovered yet. It's cleaner and more effective than drugs, but only used as a last resort.
Some people, including some nurses, think it's barbaric, and I can quite see why. It's intrusive and seems as though it might damage the sensitive brain. It's given under Section sometimes, so the patient doesn't have to consent. I have an advanced directive, in which I say I would have ECT again, even though I might want to refuse it at the time.
I spent 16 years in the RAF defending the Free World , then got bunged out unceremoniously for being bipolar. I and was subsequently diagnosed with PTSD. Funny old world, isn't it?