Duck not quacking!

So this is my ducks first winter, and I didn't want to leave him in the cold so I've brought him inside when it's freezing. He's acted pretty normal inside, and during the night sleeps in a medium sized dog pin. but today when i got up he didn't great me with his usually gusto. He was just lying down in his cage and not quacking. Which is very weird cause usually when he see's me he sounds the alarm, and at least stands up to great me.When I opened the cage and picked up up he just stood there and started walking with some encouragement, but not very far. he went for some water and has been drinking a little. but he is just standing in front of the dish, with his head kinda hunched, bill down. and he still hasn't made a single sound.

anybody have any idea's what could be the issue..?