If these signs occur, you should see a physician as soon as you can. Most virus infections causing vomiting will clear in a day or two. The main problem with vomiting is the loss of fluids. The child will frequently lose their thirst or refuse to drink because of the vomiting. That will make things worse, resulting in dehydration.
Dehydration causes a further loss of thirst and further vomiting.
From that point on things will get worse. Therefore, it is very important to push fluids hard. You should never hold fluids unless instructed by a physician. The treatment is always to push fluids hard. Watch the urine output.