Would some warm steam help to loosen the catarrah and encourage the 'number 11' under the nose to help clear things up? I imagine that it also gets worse when he lays down - I know it does for me, when I am bunged up, so I would also suggest keeping his torso supported semi-upright.
I know, I know - I am probably try to teach 'a Grandma to suck eggs',

just a thought though.
Praying for peaceful sleep for the whole family!