Does chain smoking cigarettes impair you mentally or something?

I guess what I mean is can smoking lots of cigarettes all the time make you mentally slower? This may sound crazy but even after its just been a day since I last smoked I begin to get a lot more alert, focused and mentally sharp and even more witty. Could this possibly have something to do with the Nicotine clearing my system and my lungs beginning to heal so more oxygen is getting to my brain somehow?