I would google seizures in Yorkies and find out what causes and the treatment for this... this would be the only thing that would calm me down until I could talk deeply with the vet...If it were my dog.. I would try not to leave him unattended until I got to the bottom of the situation. I would put in sick leave for monday...they know how I am about my animals...they are my family... I would just try to make him comfortable as I would do a human.
I would make sure their place is safe... I think that would be all I could do at the moment until I could research in depth about this illness