Almost two years ago I fortunately I stopped smoking with the help of Allen Carr's book 'The Easy Way to Stop Smoking'. During this two years I have been dreaming from time to time that I started smoking again. Usually I was with my workmates, having a chat and lighting a cigarette.
I usually stood there and wondered: "Hey! When did I start smoking? I think I quit smoking?"
Every time I became angry that I didn't manage to abstain the cigarettes and worried if there will be an addiction again. Finally I thought that it would have been so much better if I had never started to smoke again.
This phenomenon occurs with some quitters and is named: 'Dreams of absent-minded transgression' (DAMT).
Wikipedia quotes a study from 1991 which states a positive correlation between DAMT and successfully quitting the tobacco addiction. 
 Dream of absent-minded transgression: An empirical study of a cognitive withdrawal symptom. Hajek, Peter; Belcher, Michael; Journal of Abnormal Psychology, Vol 100(4), Nov 1991