I am very happy you took this seriously overweight Yorkie... Definately take him to the vet for a complete checkup and bloodwork.
All that extra is very bad for his oragns. especailly if he just lies around all day. It might hurt him just to try and get up and walk. It is too much pressure on his joints.
Ask the vet about hydro therapy . When swimming, it is easier on his entire body. He will be getting the exercise he needs without having to support his weight.
Also he needs to be on a low fat diet, being fed just twice a day . Offer him water all the time too.
