My Pixie gets it too, usually when she's anxious or excited. They're called Laryngospasms, and they're normally harmless. Laryngospasms are caused by a foreign body on the larynx. In response to the foreign body, the larynx tightens and spazzes, and your dog may make a wheezing sound. I was extremely alarmed when Pixie first did it -- I thought she was dying or something! But after a bit of research and a visit to the vet, I felt a whole lot better. The vet said that the foreign body on her larynx was probably just a drop of mucus or something and not to worry.

If your dog starts reverse-sneezing again, gently pinch her nostrals shut so that it forces her to breathe once through her mouth. It normally does the trick