The first thing I thought about was how drugs are used to escape reality. A nation in near total collapse would have most of the population seeking a self-medicating escape. Shoot, there are people who live that today on a daily basis. The premise that people are escaping through drug use is very plausible.
The second thing I thought about was how the drug flashback would not be embraced by 87% of the population. Why? In one word: novelty. The human animal craves and seeks novelty. The book has the hero, Nick Bottom, living his flashback time with his dead wife. He relives the same former spousal events over and over and over again. Other people doing the drugs do the same, reliving past events over and over. I'm not believing it. Why? Reliving past events would be like watching your favorite movie over and over again. Eventually you get tired of it and see what other movies are available. People are not satisfied with the same-o same-o. The hoodlums in the novel seem to recognize this. They do really bad things to people and then flashback on them. They then think about what other "fun" things they can do, making the new experiences available to flashbacking. No matter how miserable a person is now, forcing them to only flashing to their past "good" memories would be like only having five movies to watch the rest of your life. It would not be a good or fun thing, and I don't see flashback addiction being at 87%.
People would get sick of reliving their own lives, no matter how "good" they were, and go out to create new memories that they could flash back to. Addiction would be high, but it would be supported by groups dedicated to creating the "good" memories. Given human nature, the experiences would have to be like a classical drug. The experiences would have to get more novel and extreme, and in this way the flashback would be like a classical drug. Classical drugs require increased intake for the same outcome. The recreational use of flashback would require more novel experiences to justify it's use.
My $.02. What do you think?