My Dad has always slept naked. I guess that's where I get my nudism from--is him. I remember when I was about 5 years old, one night as I was getting ready for bed, going into my parent's room and asking if I could sleep like Daddy. They both chuckled and said sure. I've slept naked every night since that young age. I simply don't see the need to wear anything while sleeping.
I have been sleeping naked since I was 14, I herd from a friend that it was a more comfortable way to sleep, so I tried it and have slept naked every night since then, even when I have slept at other peoples places, I have been caught by other people, but when I explain to them that I just cant sleep when clothed, they soon understand. Its great when the weather is hot so I can sleep with no covers, just the fan blowing on me all night.
I slept in my underwear as a kid. In college, I started freeballing, and figured, "Why wear underwear to bed if I don't wear it during the day?" Been sleeping nude ever since - more than 40 years. I don't like the feeling of clothes getting twisted and wrapped up as I turn while sleeping.
I think it's good to get completely undressed each day, and let your body recover from wearing clothes. Sleeping naked is the easiest way to do this for just about everyone, even non-nudists. As a nudist, I'm usually wearing sandals and a wristwatch when otherwise nude, so sleeping nude gets rid of even those final restrictions on the body for several hours.