Reverse sneezing is common in dogs. Episodes can last for a minute or two as the dog's eyes bulge, his neck stretches and he spreads his elbows apart. You can stop an attack by massaging the dog's throat or briefly pinching off his nose to make him swallow. In extreme cases, medication can reduce the number of episodes.
Nobody knows exactly why the episodes occur, but they may be related to allergies, nasal irritants or nasal inflammation. Attacks don't last long and are not life-threatening.
For more information, please read the story Reverse Sneezing.