She hurried at his words, beset with fears, For there were sleeping dragons all around, At glaring watch, perhaps, with ready spears— Down the wide stairs a darkling way they found.— In all the house was heard no human sound. A chain-droop'd lamp was flickering by each door; The arras, rich with horseman, hawk, and hound, Fluttter'd in the besieging wind's uproar; And the long carpets rose along the gusty floor.
Madeline's up and running, and she and Porphyro begin making their way down through the castle.
Madeline's relatives are made out to be metaphorical "sleeping dragons." Now, a "dragoon" was an actual position in the British army, but the word could also be used to describe a guard. While Keats could just be being figurative—it feels like there are dragons all around—it's also possible that Madeline, "beset with fears" and already shown to be very imaginative, is actually imagining the sleeping guards into "dragons."
The poem swings back to total silence: even the drunk wassaillers (which generally means "people making toasts" and here means "drunk party-goers") aren't making so much as a peep or a snore. That silence, characterized as "no human sound," again ratchets up that feeling that there's something supernatural's afoot.
The only things that appear to be moving, apart from our couple, is the fluttering "arras"—an arras is a tapestry—as if the characters from a piece of art are more alive than the ones in the waking world.