For millenia the main source of sustenance for almost everyone in the world was carbs: bread in the west, rice in the east, maize in the new world, roughly. Most of the time they weren't malnourished.
The "withdrawal" and subsequent sustainable diet that people describe sounds to me just like what you would expect from someone making a major diet change.
The great feeling that people talk about having after a few weeks of low/no-carb diets sounds a lot like what people describe after switching to a vegetarian diet. It can be explained in terms of the sense of purity that restricted diets create (as seen in spiritual traditions dating into prehistory), the knowledge that you have the self-discipline to control your diet, and also the repleneshing of nutrients that your old diet lacked and are present in your new diet. Vegetarians often see health issues arise a couple years after ceasing meat consumption. Those who aren't carefully monitoring their nutritional intake, and some who are, get sick. It would be interesting to look at people who ate no-carb diets long-term.
I've seen ketogenic diets work for people close to me, but I'm skeptical that it's so much the lack of carbs that make it work as the self control that it forces people to exert. Maybe a vegetarian diet would be more productive if it achieves the same results, but is arguably more ethical, and definitely not less.