lethargic puppy

Question
My yorkie is 5 months old. He is usually really energetic
Today all he wants to do is sleep.
He is eating and drinking

Answer
Every dog has an off day. Does he have diarrhea or is he spitting up food? If he is just sleeping it could be that he is worn out from playing etc.
Check his gums and see what color they are and if they are pink and moist.

If they look pale or any other color then call your vet. If he is eating and drinking normally then it's probably nothing.

But if in doubt call the vet and just chat with them about it.