There are some enteric problems this might be... so my first, easiest suggestion is to administer Epsom salt to the water (a level teaspoon per ten gallons of system> I can only assume he has gulped air at the surface and can't expel it. <Maybe... but doubtful. Much more likely so...
In the meantime, there is no harm in trying some epsom salt soaks 2-3 x per day until your vet visit. This may help to reduce the inflammation. I hope Sam does ok! Dr. Marie. Warning: Undefined variable $displayed in /usr/home/drmarie/public_html/askavetquestion.com/answer_np.php ...