“For they sleep not, except they have done mischief; and their sleep is taken away, unless they cause some to fall -- Proverbs 4:16.”
Most likely I'm way off base but the passage sounds dire to me. Like a warning of sorts. The "they" who "sleep not" sound like undead (like the one suspended by the chains). They don't get to sleep (stay dead) because they've done mischief (some sort of evil). So their sleep is taken away (reiterating that they don't get to go onto the next world), unless they cause someone else to fall (corrupt a living person, turning them into a wraith?).