Many people have similar and recurring nightmares, probably often rooted in societal taboos,
like "I was changing before gym class like everyone else and I ended up being the last person to finish, then as I entered the gym hall, everyone stared at me and started laughing and pointing, so I looked down and noticed... that I was actually completely naked!".
Well, that... isn't a nightmare I remember ever having, but that actually happened to me in probably 2nd grade.
I had somehow forgotten to actually put clothes ON.