Last year when I quit for 6 months (my longest time!), I owed it all to the Chantix. And I didn't have a single adverse effect. It worked wonders. I didn't crave, and I didn't miss. Magic beans, I swear.
But when I tried again this year, I took Chantix for a week before I started experiencing the vivid nightmares and then had anxiety attacks.
The trick with the vivid dreaming is that while you may not mind the nightmares, they are depriving you of REM sleep, that deep deep sleep that you're supposed to be rolling in and out of every 45 minutes or so. You never fall into that deep sleep and thus are never fully rested and refreshed. The profuse night-sweating that I also experienced certainly doesn't help.
But you know what did help? You're going to think I'm crazy. But a nice tall glass of wine before bed works wonders. I don't know what it was about it, but the dreams became less vivid and the nightmares less terrifying, and I slept like a widdle bebe. (Of course once I started getting the heart-pumping anxiety attacks during the day, my brief rekindled romance with Chantix was over, finito, zippidy-doo-dah done.)