3) Loss of privacy. This goes back to discourses on social media, common sense, the diminishing of the term "friend" and crowd-sourcing. When I was in high school, you held sleepovers with maybe a half-dozen of your close friends. They were the ones who got to meet your parents, annoy your siblings, chase your pets, hang out in your room/closet/basement (whatever), and watch movies/talk/crimp hair late into the night. It was a fairly exclusive experience that could be shared second-hand at school the next week in discussions. It allowed for safe risk-taking, potential embarrassment that was understandably manageable because of the small number of witnesses. Nowadays, if sleep-overs do still happen, they are streamed, tweeted, shared, and updated so persistently, nothing is sacred or safe anymore. And, similar to the word "friend", "privacy" in this arena has become so de-valued that the approach has become extreme - either you share everything or you share nothing at all. ever. Neither is really healthy emotional development and both can be potentially problematic socially.
To end where I started, PJs are a source of comfort in theory. I have my winter PJs - red fleece reindeer printed ones and seafoam green fuzzies that I refer to as my Muppet-skins - and a couple of sets of cotton coordinates that appeal to my humour (see today's) and my own personality (see today's). PJs may, in fact, in their natural state (ie. not-Spirit-Week requirement), be a source of truth for how we see ourselves. I believe we sleep best when we are at ease and there is some evidence that we learn best when at ease too. However, the jury's still out on how well teens learn while asleep.