I had a lab mix who reverse sneezed regularly. I was never able to figure out what triggered it, if anything. She would look anxious while it was going on, and comforting and rubbing her seemed to help. She lived to 15 1/2, so it had no effect on her overall health!
When she was older, she also showed up one day with what turned out to be vestibular syndrome, which is infinitely more scary to see than reverse sneezing, but is also one of those things that comes from nowhere and generally resolves itself (but it takes a few weeks). Look that one up, so you’ll recognize it if you see it.