hi tat, lil t. didnt have a cold, his lungs were x-rayed for tumors but showed no signs of any disease. my vet thinks it's an allergy and he has already explained in volumes how a permanent treatment will look like.
but i remember that t. had a cold once when he was younger and he showed all the signs that you mention above. it took him a week or so to get through it. has your priest already got his cat flu injection? but it could also be an allergy. just let your vet take a look at him.
if you have a cat transport box, you can put priest inside. then you put a pot with warm camomile tea in front of it, maybe place a towel over the box and then make sure he inhales the not too hot air. never use any essential oils, they harm the cat's respiratory system. there is not much else one can do. if it gets worse, your vet will probably give him antibiotics.