Well then, this is an awkward fantasy by Flash Sentry when he heard about the Sleepover Twilight had with the other Mane Five and Sunset Shimmer when she was staying during Rainbow Rocks, imagining them wearing less than modest sleepwear. Big Macintosh is not happy with Flash when he surmises what he is fantasizing about.
Just a silly idea I had when I saw the Sleepover base. I didn't think i was likely they would all dress that way when sleeping, bu it doesn't mean someone might not try to fantasize about it.

I made this picture from bases made by found here Equestria Girls Slumber Party Base , here Equestria Girls Flash Sentry Base and here Equestria Girls Big Macintosh Base