mean hairball or emphysema?

Ok, so Mom's threatening to drag me back to the vet's office. Someone has to have an idea what this might be. Every three or four months I'll do this thing that sounds like a cross between the meanest hairball ever and an emphysematic cough. When I'm having an attack I cling to the floor like I'm going to fall off and with each "cough" I wretch my whole body. I never produce any hairballs and don't have any symptoms of an URI. Each episode only lasts a few seconds. Mom's mentioned it to the vet in the past and he said to watch and see if it gets any worse. I've lived here w/ Mom coming up on five years now and my pattern hasn't changed any. I've been tested for FIV/FLV and both came back negative. Anyone else do anything like this? Oh, yeah that bratty lil sister, Izzy, is still up for sale...any takers? -Jordan