I've been a full-time nude sleeper since my teens. It's gotten to the point where I don't even think about it, and if I have to wear something (sharing a room with someone who would mind nudity, or sleeping on a friends couch or something) then I never get as good of a night's sleep as I do nude.
I used to always wear trackpants or pj bottoms even though I would actually prefer nude when I was in shared accomodation situations ( other guys and/ or gals I am not in a relationship with.. Why? I dont want to have to cover up if I need to get a drink of water or take a pee but mostly because I have an embarrassingly tiny penis which I went to great lengths for no one else to see. If and when I had first time sex with a girl I used to make sure they didnt see my flaccid size before or after sex. After getting it on I made sure I snuck away to don something to cover me so they wouldnt see my tiny dick in the morning. One time I awoke without the cover of pants or a cover and the girl I had slept with was actually staring at my tiny cock with what looked like a cross between shock and dismay. ( it was akin to waking up with a girl whom you drunkenly flirted with at a bar or party and saw she wasnt your type at all.)