My dogs legs were lke jello and he could not stand or walk then he threw up.What could be wrong with him?

Last night my 4yr old Yorkshire Terrier got up to walk and could not walk or stand.His legs were like jello. I was worried, I held him for about five minutes and when I layed him down he threw up and then seemed better. I am worried, has anyone else experienced this? Is there something wrong with him?