It’s one of the greatest of all dog owner mysteries: What the heck is a “reverse sneeze”?
Veterinarians know it as the “pharyngeal gag reflex,” and while it can sound like your dog is about to keel over dead, in almost all cases, it’s harmless and requires no treatment (although you might want to try earplugs!).
What causes it? Throat irritation, mostly, sometimes from cold air, others from food, water, or allergens. The dog extends his or her neck to try to clear the feeling, but in doing so, narrows the throat. It’s harder to get air in at that point, and so the dog breathes harder, narrowing the throat more.
Small dogs are more prone to the problem, most likely because their throats are smaller to begin with.