Withdrawals
I applaud the person who is trying to get off of drugs or stop smoking. Either one has the potential to extend life. The possibility however does exists for them to have withdrawals because their bodies have been conditioned to depend on something that alters emotions.
New Christians have withdrawals from time to time. They think about the things that they use to do before they got saved. If not nipped, the new Christian can go into a stage of depression or simply backslide.
Romans 6:11-13. Likewise reckon ye also yourselves to be dead indeed unto sin, but alive unto God through Jesus Christ our Lord. Let not sin therefore reign in your mortal body, that ye should obey it in the lusts thereof. Neither yield ye your members as instruments of unrighteousness unto sin: but yield yourselves unto God, as those that are alive from the dead, and your members as instruments of righteousness unto God.