I noticed during playtime a hacking/gulping sound. He stopped running and seemed to want to vomit. it lasted maybe 15 to 30 seconds. I thought it was a hairball or him trying to vomit something up but nothing was produced. Once it was over he gulped and began to play again. Running about like nothing happened. There was no wheezing/rattling noise during the episode. I haven't noticed him panting or any shortness or breath. what could it be?