To the person who asked the difference between these 2, I will offer my answer. A slip is when you have a smoke or very few and then get back on trying to quit again. A relapse is when you have a smoke, then more smokes, then you buy cigarettes again and are right back where you were before you quit smoking. I will add as you age cigarettes do affect breathing, and if you wake up during the night, your oxygen level will be lower. It does not show reall while you are young, but it increases as you age.