Hi there yes that's how suction works! Been there done that - NOT fun! His throat may feel obstructed by the swelling - and tightening caused by the radiation as well - right from the outset mine felt very tight and didn't loosen up for some time after I was done treatment! Mine is still not completely normal but believe it or not yawning helped! It stretches those muscles. I gagged a lot as well from the mucous best recourse is to Spit it out. (seriously I used to hack it out constantly - ) take a cup or something
Grab the salt water / baking soda mixture rinse gargle and spit it all out. This sets the baking soda down farther than just a swish which helps heal, and helps clear out the mucous though I have to say I fell totally in love with my water pik during this time, I picked up a natural mouthwash with no alcohol in it - I would add a little bit to Lukewarm water in the waterpik canister turn it on the lowest setting and blast it around my mouth - it would clear out all the goup, and make me feel fresh for a bit. It was also a great too for keeping the mouth clean and avoiding infection.(I used it after every meal and before bed! Best of luck! Also i know his throat is tender but tell him to get a big bottle of club soda - leave the lid off it, and stir it frequently until it goes flat, cover the opening with something though to keep stuff from getting in it (paper towel?)- once its flat you can cap it - leave it at room temp so i left mine on the counter - he can actually drink this which is great because it acts the same way as the baking soda mixture but it goes all the way diwn, helps preserve the swallowing reflex, gives him fluids, and clears out some if the mucous! Tell your brother to take care - he can do it!