O my gosh! How scary! Did the vet give any clue as to what they think is causing the problem? Do they suspect something wrong with an organ (being that you mentioned pancreatis)? My cocker went through something like this when she was about 10 or 11 years old - didn't hold anything down for several days. We were very scared. It turned out that she had twisted her back funny and was in pain. Anti-inflammatories and painkillers for a few days, and then she was back to normal.
I'm praying that Hannah's problem is just as simple to fix!