Is it, though? I ask because my father smoked himself to death and the only time I ever saw him breathe deeply was when he inhaled on a cigarette. I wonder how much the deep breathing part of smoking produces the feeling of calm. Apart from the need to get a fix because of the physical addition. First it "relaxes" you, and then you can't relax without it. In the end, it can't truly be a stress reliever because it actually exacerbates stress and anxiety.
It is actually, cigarettes can be very calming to an agitated person, knowing you can pop out for a smoke and fizzle some cyclic thought away is a comfort quite often. My mom got lung cancer from smoking, even at the end she said that cigarettes where her "friends in a way". She had a great fear of dementia and she played the odds well, passed at 70, no dementiia But clearly it's swings and roundabouts, as the health toll grows, emphysema is a big alarm bell for many.
I fall to sleep easy but sometimes i feel my cortisol spikes at around 3 am. what I do is up go to my meditation room. meditate for 20-30 mins. When i mediate i just think of me sleeping, go back to bed and sleep like a rock.