My sister smokes a couple packs a day and she really has a hard time on flights although they are just a few hours long. I never flew back when smoking was allowed. I couldn't imagine being in an enclosed area breathing in someone else's secondhand smoke. It is bad enough when you get a non-smoking room at a hotel and the person before you decided to smoke in it. There are many considerate smokers but at the same time, many that are not.