Reverse Sneeze:
"Reverse Sneezing" and "Hacking/Gacking" are both symptoms of swelling in the sinus, and the back of the throat. With "reverse sneezing" the problem is PARTICULARLY the "soft palate" which is swollen by air quality (cold, dry, overly hot and dry, polluted, smoker at home) --- and then the swelling in the soft palate makes the 'epiglottis' "stick" over it. They have to make 'sudden, explosive' inhallations through their noses to dislodge it. It's NOT life threatening but it can go on for several minutes. Sometimes sounds like they're tryna hawk up a loogey.
All you do is reduce the swelling, humidify the world if possible, and SOMETIMES if things have progressed to sinus INFECTION (as evidenced by 'not-responding' to conservative care, we add an antibiotic.)
Once in a "blue moon" you have to dig deeper and Xrays of the sinus and throat (even a sedated laryngoscopy) shed light on these oh-so-common cases.
Doc Johnson
PS: It's easier to arrive at this presumptive diagnosis with a video, and if "pollen season" is afoot.