I actually stopped taking my chantix after week 2 because I was experiencing difficulty with my sleep. I couldn't sleep well, and when I did, I would have wacky and sometimes scary dreams. The last night I took them, I had this horribly demonic dream which centered around where I grew up, and I didn't want any part of my brain stealing away my happy place. So, I stopped taking them, and I am fine without them, and my sleep has much improved. My doctor even told me if I felt that they were having negative effects on my body or psyche in any way, to stop. My mental and physical health were too important. My sleep is better, If only my husband would stop waking me when he swears I'm snoring.
I sometimes get cravings for cigarettes, but the chantix helped me over the road block of the first couple of weeks. Now, I'm quit for good, and when I want a smoke, I think of how hard it was to quit in the first place, and realize it really is NOT worth it at all!