I can't smoke in my house (except for the basement/garage) so smoking in bed is a nonissue for me. Even if I could, I wouldn't!
I've come close to falling asleep smoking while sitting in a chair by a camp fire, so I imagine that it would be very easy for me to fall asleep smoking in bed.
When I was growing up, my grandparents on my Mom's side were cigarette smokers. I remember very well the burn marks on the arm of my grandfather's recliner and my grandmother's couch from where they had fallen asleep while smoking! I also remember their mattress having holes burnt into it!
I can't imagine why anyone would want to take that risk!