Q. My dog is 6 years old and a terrier mutt, he was laying down last night and started yelping and shaking, nothing seems to hurt him
DESTINI R. HOLLOWAY, DVM
A. This sounds like a possible seizure or musculoskeletal issue. I would recommend monitoring him for now to see if this event occurs again. If it does, record the even on your smartphone or recording device so that you can take this vital piece of the puzzle to your veterinarian so that they can see what you saw.
Based on this and a complete physical examination your vet should be able to point you in the right direction towards possible diseases and an appropriate treatment plan.
I would also ensure that you don't have any toxins or potential chemicals in the house that could be causing this suspicious behavior.