I had a somewhat different experience. I started eating low carb, but not keto, and did not experience any flu or withdrawal symptoms. I then switched to an Atkins 72 and got into ketosis, and also did not experience a that time. I have mentioned before that after reaching my goal, I experimented a lot going in and out of ketosis, and for the first time I did experience flu like symptoms getting back into ketosis. For me anyway, I think it was something more complicated than an addiction to sugar or carbs.