I used to get a headache when I didn't have enough coffee within a given period of time. I assumed it was because the coffee thins ones' blood, mucus membranes, and other fluids. By not having an injection of sinus fluid thinner, my sinuses would by slightly blocked, causing a mild headache which would go away shortly after a shot of espresso.
But I've recently realized that the above logic is incorrect. I'm on day number 5 of not smoking, and I've been having those same headaches, only I've been having coffee. The headache is a withdrawal symptom. I've had to fight a small handful of cravings, and talk myself through a few tense moments when I got around to questioning my decision to stop smoking. I certainly have learned a few things about myself along the way as well: I find it very easy to not smoke with other regular smokers, turning down office smoke breaks, and smokes with friends on the weekends; but I find it really difficult to not have my solo smokes in the evening after dinner.
I've also learned that smoking is a deep breath regulator. In the last five days I have found myself feeling tense, fighting a headache and thinking about whether or not I'm hungry or just needing to keep my mouth busy. Stopping to take a deep breath suddenly seems to make half the tension go away. I wonder why I don't do that more often, and now I understand why I always hear people sigh on the subway or in the elevator.
I'm not worried about whether or not I'll be successful this time. I'm just hoping the headaches and the moodiness goes away in a few weeks.

What I find really interesting is how I am reformatting the synaptic pathways in my brain. Satisfaction and gratification no longer come from the same set of behaviours, and gradually my brain will adapt. I thought this was well depicted in the film
What the Bleep Do We Know? Which leads me to think about what I can train my brain to take gratification from. Some say to replace the nicotine with adrenaline (the runner's high, exercise). I'm wondering if I can convince myself that having a cramped back from hunching over a laptop is a satisfying feeling.