Welcome to the forum....What do you mean, he can't lie down? Can you describe how he holds his body???
Do you by chance have an emergency vet anywhere around you??? Let me know...Thanks
Pugs are notorious for gobbling their food and not knowing when to stop. They are also notorious for serious gas issues involving not just bloating but also severe flatulence. Pug farts are the stuff of legend.
He probably swallowed a lot of air when he was coughing, but he should have started to deflate by now. If he is having trouble lying down and some breathing difficulty, a visit to the vet is definitely in order because pugs have enough trouble breathing due to the brachycephalic structure of their faces, they don't need help from trapped gas.
You can try giving him a couple of bites of raw carrot. This sometimes helps to relieve the gas. It also, when you call to make the vet appointment (which should be TODAY), couldn't hurt to ask the vet what you can give him in the meantime to try to relieve the gas and bloating. Pepto Bismol can be given to dogs but ask your vet what the dosage should be based on your pug's weight and age since he is a senior dog. This will hopefully make him at least a bit more comfortable until you get to the vet. Switching his food to something different than he is used to can also sometimes help to lessen gas. If you feed lamb, switch him to a chicken based food. Avoid foods that contain corn. Avoid liver treats and liver based foods, they are horrible contributors to gas.
The most important thing to do RIGHT AWAY is to CALL THAT VET AND MAKE AN APPOINTMENT. Please stop back and let us know what the vet said and how your boy is doing.
Ghilly