I did not experience all the symptoms myself when I quit, but when I was involved with the American Cancer Society/YWCA stop smoking clinics, many of the successful members reported all sorts of wierd symptoms from the expected nervousness, irritability,etc. to less frequent but not uncommon constipation, head aches, and yes, even a feeling of constricted breathing and/or unwellness.
As it takes up to 21 days for nicotine to clear the system, it is probable that Bill is right and your body is doing its final whine to be fed nicotine, but please do check with your doctor just to be on the safe side.
Nobody was reporting wierd symptoms due to not smoking after the first three or four weeks, and the best pleasures of not smoking usually start kicking in about then too.
Gold stars for Bill, Jer, Kristie!!!! Another successful week completed.