If this happened right after the dog had a really fatty treat it might have been a pancreatic inflammation but blood work should have found that.
However there is a medical issue commonly seen in toy dogs called HGE or hemorrhagic gastroenteritis.
You can read about this here
http://www.gvsvet.com/hge.htm
It could have been a food poisoning episode if the dog was given any 'old' meat or a cold cut to eat. Listeria, Campylobacter, Salmonella and other protozoan or bacterial diseases can cause these symptoms too. One of my vets years ago called it 'garbage poisoning'.
You did great getting her vet care fast and even though it was costly that probably saved your pet's life.
I wish I could tell you a prevention but there just isn't one other than not giving fatty treats or 'off' meat the HGE just has an unknown at this point trigger.
Hope this helps you!
Edited by NHolmes on January 16 2006 at 12:26 PM
Please press Accept if you find my answer helpful. Want more info? Just reply on your question!
Bonuses for good work are always appreciated!
Thanks for the opportunity to help you!