Thank you so much for your reply, Wylie's Mom. After I posted the message above, Rigby had no further problems. This morning, his feces was well formed and he had no vomiting since. He spent a quiet and uneventful night, and appeared to have "got rid" of anything that was bothering his tummy.
But I'm not taking any chances. Today, I had an appointment booked with the vet for a general check-up, and I will keep it. I will tell the vet all that I told you, so Rigby has a thorough examination.
I am thankful that I stumbled upon this site. Although I showed dogs for 18 years (Springer Spaniels and Cavaliers), I realize that I know very little about Yorkies. What a wonderful place to learn! Your efforts are very much appreciated!