Actually, there are documented side effects of Chantix, similar as described above. They usually occur in people who have already been battling depression or anxiety. It is not prescribed in some cases, to people with that history.
A doc from MGH came to my clinic to pitch participation in a stop smoking study to the clients. They are trying to figure out why so many people with mental illness, especially schizophrenia, smoke. The study uses Chantix, and she addressed this issue. She said that were a bunch of cases of these side effects when the drug first came out, but now, not so much.
But still, it's a caution.
I still remember when my mom quit cold turkey, when I was in 6th grade. It was ugly. She started smoking again, about ten years later, but she did quit, cold turkey, again eventually. My dad, on the other hand, is about to turn 85, and has smoked for like 60 years. He hides it now, though. He had one mild heart attack, 2 years ago, but other than that, his lungs are fine.