I was raised in a very 'open' home environment - hippy parents - so nudity was very common and as a family we all slept nude - so I have been sleeping nude all my life - where I live it is tropical all year round so sleeping nude is very natural and comfortable for me. I enjoy the freedom and the comfort of sleeping with nothing on. In the cooler months I may need a sheet.
My parents certainly weren't hippies and I never saw them nude but did on occasion see them in their night wear - several layers of it in the case of my mother. I'd have thought that most people who sleep naked would put something on to wander around the house - eg an early morning coffee or a late night drink between showering and going to bed but perhaps people fully relaxed with nudity would just stay bare ?