You know those extra tree straps that come wit the stand's FAS, just flap one of them around your torso and the tree and you don't have to worry about falling out. When I was a kid I never wanted to nap, I changed my mind and wish I could have all of those back.
if it's a morning sit; guarantee there wil be a nap unless I stick one by 9am or so...and even then if I got there before sunup there probably was one before dawn as well. I almost never nap on an afternoon sit...but will catch a Z or 2 mid day on an all day sit.
I always take a nap when I hunt all day. I'll go to the truck eat then take a thirty. When I get to the stand at 5am I spend a lot of that 1.5 hours napping waiting for shooting light.