Yes, and I had tried several times before, without success. The difference is that earlier I just wanted to stop smoking for health reasons, but I still loved smoking. After reading the book, I don't want to smoke because I just don't like it anymore.
Taking Alexander technique classes improved my posture a lot, and cured the tendinitis I used to get in my shoulders.
Reading https://www.amazon.com/Allen-Carrs-Easy-Control-Alcohol-ebook/dp/B07B7QRWTH enabled me to quit drinking alcohol very easily. It was almost like it just turned off my desire to drink for good. ~3.5 years alcohol-free now.
Reading https://www.amazon.com/Allen-Carrs-Easy-Stop-Smoking-ebook/dp/B0051XSN50/ enabled me to stop smoking very easily, and I've not wanted a smoke in 25+ years now.
I'm missing Allen Carr's book (https://www.amazon.com/Allen-Carrs-Easy-Control-Alcohol-ebook/dp/B07B7QRWTH ) in the list of books. I quit drinking after reading that book over 3 years ago, and it was almost like flipping a switch, so fast did it turn off my desire to drink.
Almost half a century ago, when I was 16 or 17 and still believed in God, I went to a synagogue with some people of my church for some kind of exchange thing. The service was quite boring though, as everything was in Hebrew and I didn't understand a thing. But there was nothing to be done except sitting still trying to be respectful. So I guess I fell into some kind of meditative state, and I don't remember anything about that, but just afterwards I felt that I had been in the presence of God, and a sense of great gratitude. I'm still surprised I didn't convert to Judaism on the spot; maybe I would have if I weren't so shy...
OK, I'll go first. I'd correct people's grammar and spelling a lot, and I'd tell overweight people how to lose weight.
Oh wait, I misunderstood the afterimage thing. No, I usually don't see them while I'm looking at something, only when I close my eyes or look away. I do sometimes get the effect you describe, but not often. I tried to see the 'snow' again just now, but I didn't see any.
I took 10 lessons, and I think I could probably have done it with 8. I still feel myself sagging now and again, and then I have to correct myself (and then I wonder why I sagged to begin with, because the correct posture is actually more comfortable). I have also bought a new chair ( https://www.ikea.com/nl/nl/p/kullaberg-bureaustoel-zwart-90325518/, only mine has a different color) and removed the backrest. I have found that chairs with a backrest and armrests tempt you to lean on them, and then you can end up sitting in a wrong posture for a long time without noticing. Without them, I soon notice and can correct myself.