I want to attach a comment here from our thread Giving and getting medical advice online
I normally tell people who experience wild or bizarre reactions the first few days not to be surprised or unduly alarmed, it is likely from not smoking. But at the same time they should not totally ignore certain symptoms, in case in the long shot that something else is happening just coincidently at the same time as they are quitting smoking.
The symptom of muscle tightness is often felt through out the body. Back aches, neck pains such as those experienced from times of extreme stress, even leg cramps can be felt by some. Chest tightness too can be experienced. While quitting smoking is the usual reason behind the reaction, for obvious safety reasons it is prudent to get the symptoms checked with ones doctor. You just don't want to take the chance that you were the exception to the rule, that the chest pain was actually a signal of real heart trouble.
I have literally had over 4,500 people in smoking clinics over a 26 year time period and had only had two people actually have heart attacks within a week of quitting. And they were both people who were quitting because of doctors advice that a heart attack was an imminent danger because of pre-existing conditions. So while I am not trying to say that the risk of a heart attack is high from quitting, in fact your risk of heart attack decreases upon cessation and relatively quickly, there still is a risk as there is with all smokers, ex-smokers and even all never smokers. Ignoring a cardiac symptom is just an unnecessary risk that no one should take. It is better to check in with your doctor and to be safe than sorry.
Doctors are often very receptive to work with a person when they are quitting for they often recognize the serious nature of the effort.
So as for symptoms, don't be surprised or alarmed by anything, but be cautious and stay aware. If you experience any symptom that would normally be a reason to get checked out immediately, follow through with the same expedience now. Life goes on without smoking and things can always happen.
Also, once over the first few days, be really cautious of blaming symptoms on smoking cessation.
While some reactions can linger, especially coughing and excessive phlegm reactions, other factors can happen too, especially during cold and flu seasons. Pretty much stay aware and follow the normal precautions you followed before while smoking. Unless as a smoker you never did anything, for some smokers are intimidated to go to the doctor when having symptoms for shear embarrassment that the doctor would just chastise them for smoking and tell them to stop. Rather than putting up with the admonishments, they would ignore problems in the past.
As an ex-smoker you won't face the same complications. Again, doctors are often more prone to work with you when they see you working for yourself, and not to ignore symptoms writing them off to a normal smoker's ailments. They are often more supportive when you quit.
So to stay healthy, learn to listen to your body. Smokers are notoriously bad at this, for their body was likely telling them to quit for a long time and they ignored it. But the day the quit smoking was a good indication that they were now working with their body to maintain health. To keep a good partnership going with your doctor, other health professionals, your family, friends and your own body always remember to never take another puff!