How do dogs behave while pregnant?

Let's think about it. If you were pregnant with 5 puppies (not saying that she will) and you had to have them stuck in you for a long time, I think I might be tired. You don't need to worry if she sleeps, she will get more tired than usual, but if she sleeps nearly all the time and doesn't bother to eat you might want to check in with the vet.