(It’s really difficult to tell what’s going on here without some code. My guess is that you left out [regarding the noun] and Inform is going a bit crazy trying to find the referent of “They,” but it’s also possible that you’re referring to some global variable that you only set when you zap something.)
Well, I wasn’t sure what you had before “[the noun] [are] asleep.”
By the way, you don’t need “now the sleeper is the noun”–your header line “After examining an asleep person (called the sleeper)” automatically sets the sleeper to whatever you’re examining. (That’s what the “called” line does–creates a temporary variable that’s initially set to whatever you’re citing in the header.)
Anyway, chapter 14 of the documentation on adaptive prose is well worth looking at. That’s where you’ll find the “regarding…” trick, as well as the “[They’re]” substitution.