For most of this movie Stan walks around in a funk, but by movie's end he's being affectionate to his wife again and seems to be smiling at work while he's stampeding the sheep to the slaughter. Why the change in mood?
shareHe finally got to sleep.
shareYes, I would like to know this, too.
shareThe end of the film reveals us that the only thing that makes him smile any more, is the killing of sheep. You can interpret it however you like. I think it shows him getting out of touch with his humanity.
He was also suffering from insomnia - he was killing the sheep he should be counting, at night.