Hi Iain, I'll answer your posted questions first before weighing in my opinion.
I quit smoking cigarettes several months before begining aikido, but continued to smoke cigars, at times casually, at times habitually and regularly. Over time I found that the cigar smoking was interfering with my ability to train as hard and as long as I expected and wanted. I made a decision to stop smoking cigars regularly, I now keep it to a minimum (at most one a week in the summer months.)
Reality - nicotine dependence is a tough monkey to shake. If you're serious about quitting and are having withdrawal symptoms, I recommend seeing your doctor for nicotine replacement therapy and start working a chemical dependency recovery program until you are solid in your non-smoking status. After 13 years I still, on rare occasions, have cravings for a cigarette. It's a tough addiction to break, but it can be done. Best of luck in your efforts to make changes in your life.
I get to Baltimore occasionally, hope to see you on the mat sometime, or come to AWR when Charlie Sensei comes up this Dec.