PLEASE HELP: POODLE BREATHING PROBLEM

My toy poodle just turned 2 years old.  He is full of life and all the vets that he has seen seem to think he is absolutely healthy.  When he was about 8 months old, he crawled under a bed and came out completely covered in dust and webs and what not.  He immidiatly started making this weird loud labored sniffling noise (his mouth was closed so it was coming from his nose) which sounds very much like a child that is sobbing uncontrollably and trying to breath at the same time (you know that fast labored sniffling thing that kids do).  It freaked me out and as I was about to jump in the car to go to the emergency animal hospital, he stopped making the noise (which had lasted for about 3-5 minutes) and all was fine.  Since then, he occasionally makes that noise, maybe once or twice a month, but it seems to take longer than the 3-5 mintues the first time I noticed it.  My house is pretty clean, but I suspect allergies could be the source of the problem.  However, last night was really bad.  He started his sniffly noise thing around 7:30 and it continued for about an hour and was accompanied by dry heaving until I was afraid something was stuck in his throat.  I held him upside down for about 15 seconds and gently padded him on the back and he produced a gigantic amount of vomit which was SUPER foamy and oily and sticky in consistency.  It kind of looked like a cracked egg.  He was fine for about 2 mintues and then started sniffling and produced even more of that egg-white foamy oily vomit.  So the sniffling continued for about 5 minutes more and I decided to see if he could bark so I showed him the signal to bark and as he attempted to release the first bark he made this deep burpy suffocation noise and bent down on the ground as if he was bracing himself.  I honestly thought that I had killed my dog, but about 5 seconds later he regained his breathing and continued his sniffly noise through the rest of the night.  I called the emergency animal hospital and they didn't seem to concerned about the issue and told me to make an appt with my vet the next day.  The problem is that I have taken him to the vet regarding the sniffling problem several times and each time the docs say he is healthy.  I cant induce the sniffly noise he makes at the vet, and I cant get to the vet the moment he starts making it so I think I will just videotape him next time and take that to the vet.  Anyway, back to yesterday's incident.  So the sniffling lasted for several hours and became less and less prominent until he went to sleep.  He slept fine all through the night and then this morning made the sniffly noise 2 or 3 times until I had to go to work and couldn't be with him anymore.  During the incident I used my stethoscope to make sure his heart rate was fine (it was normal and regular) and I tried to listen to the lungs to hear if they had liquid in them and everything seemed fine except for the loud noise I heard everytime he made his sniffling noise.  So basically my questions are what is going on with my dog and has anyone ever heard/experienced this before with their dog?  Also, aside from rushing to the emergency room, what should I do that could potentially help him?