Is your chi vaccinated against kennel cough (bordetella)?
If not, it may be kennel cough if he's been around other chis lately that might have had it or was at the vet or in a kennel situation.
If not, like 8Batch said, 1/2 a baby aspirin or benedryl (1 mg per pound every 6-8 hours - my first aid book says to use adult benedryl, not pediatric with those dosages) should help. Also, if you are scared that he may be getting dehydrated, you can offer him a 50/50 mix of water and either pedialyte or gatorade.
Give me the symptoms and I'll look it up in the first aid book for you. (I love this book! LOL)