We have been having this problem with Bentley....had him at the vet last week for it again and if it continutes he's going to have to go through the run of tests. Sounds like your dog is doing exactly what Bentley does...he had a bad episode last week and we rushed him to the vet. It's been an ongoing thing here too off and on and I've been really worried about it. He hasn't thrown up in about three days now...but just like you said..he can go a week or so without doing it, but then it's back again. We've tried everything and if it starts again he'll have to go in for tests.
Please keep an update on how Reese is doing and what your vet says as I'd really like to know as well. Feel free to PM or email me!!! I'm reading that article now that feminvster posted.