Welcome...I agree w/Margot....We have no way to diagnose your girl on a public forum.....She obviously is in severe pain! Dogs are good at covering pain until they no longer can stand it! Everything you describe is PAIN!
This could be anything from a Spinal injury to Pancreatitis (Which can be fatal if left untreated).....
Is she drinking water? You need to keep fluids in her until you can see her Vet....Dehydration alone, can cause an array of problems....Small dogs are more at risk!
Once you get a diagnoses from your Vet, then we will be able to help you with why it happened, the causes and how to avoid it in the future...Until we know what's wrong, we cannot just guess.....
Please, call your Vet and get her an appointment today & get her some help!!! She needs to be treated.....Let us know & good luck, Karla
Sounds like she is in pain or major discomfort, not sure if it internal, possible spinal problem, etc.
I think you had better get her in to see the Vet to determine what is going on.