Reverse sneezes have the same cause as a regular sneeze but are much more dramatic!
You should look around the home for allergens and eliminate them if you can. Carpet powders, cleaners and pollen are pretty mean culprits.
I found an informative article that might explain it for you better than I can.
Paroxysmal Respiration or "The Reverse Sneeze"
I have found evidence that the massage technique mentioned above works well as does forcing the dog to swallow.
Let me know if you still have questions.
Some dogs will do this for a lifetime and others will have it flare up at odd times. To help it, you can try adding some moisture to the air and do all the things you would normally do if it was a regular sneeze that went on again and again.
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