
When Buster was a pup he had somehting similar, allthough it never effected his breathing. He woke from sleep and his eye lids had drooped so far down I couldn't see his eyes, when inspected his eyes looked sore and they appeared painfull. This was quickly followed by loads of salivation (much, much more than normal Mastiff slobber), panting and when he tried to walk he appeared drunk.
I had him rushed to the vets, at first, by looking at him they thought he had been poisoned

That was soon ruled out & they kept him in for a few hours under observation but still were unable to find anything causing it. I picked him up later that day, when he was much better (apart from some soreness in his eyes) and the vets could only assume it was some sort of allergic reaction to an insect bite.
It happened once again a few days later. Then it never happened again (this was over 2 years ago now).
Both times it started when he was on the sofa, so I had tore my living room apart looking for any possible offending bugs. I never found anything. It drove me mental not being able to pin-point the cause and for weeks I followed him around the garden watching him like a hawk in case he was getting bitten out there.
How frightening that it's so bad in your dog it's effecting her breathing :(
I can understand how you are feeling, it makes you feel completely useless :( :(
Best of luck.