I've always handled caffeine well; 5+ coffees per day, no anxiety. I get hypoglycemia symptoms no matter how often I eat, but I have to say that I don't think the nicotine anxiety was from hypoglycemia because it was more of a low-level anxiety that persisted throughout the day regardless of other symptoms. What dose of niacinamide did you take?
I use 500mg whenever I take caffeine. It helps shut down cortisol/adrenaline response and provides GABA agonism. Theanine could also be used or glycine/gelatin too. I read that nicotine can increase glutamate so theanine might be best.
I'm curious on @haidut 's view regarding nicotine/smoking. I know he is European so he at least had to smoke at some point in his life lol...