Every night, we make the Berachah of המפיל חבלי שנה על עיני, Who causes the binds of sleep to fall on my eyes (Berachos 60b; SA OC 239:1), and in the morning, we make the Berachah of מתיר אסורים, Who releases the bound, which refers to when one sits up after waking (Berachos ibid.; SA OC 46:1).
Why don’t we just say “He Who causes us to fall asleep” and “He Who allows us to sit up”? Why do we use such a metaphor instead of a more direct terminology? What benefit is there in describing sleep as being bound, rather than describing sleep as sleep?