Ask a Dog Vet and Get Answers to Your Dog Health Questions
Unisom comes in a few different formulas. The ones that are just sleep aids should be safe, even in a Yorkie, as the active incredient is an antihistamine. Dogs do well with these drugs. However, there are a few that contain acetaminophen which is not a good drug in dogs. If what you have is a sleep and pain med combo, really, it should see a vet ASAP to ensure we don't have kidney or liver toxicity. So the answer really lies in which version of Unisom your little buddy got into.
Hope this helps. Please don't hesitate to ask for more details if I have not explained this thoroughly. Sleep aid... should be fine. Sleep with pain... not so good.