Animals do not have this problem. No, he doesn't. As soon as he begins to feel tired, he will drop everything and go to sleep. Right on that very spot. In fact, if a dog were to jump, then realize once he got up in the air that he was tired, he would defy the laws of gravity and go to sleep right there.
Humans are slightly different.
We fight sleep as if it was our mortal enemy. First there are the head spasms. Your chin makes contact with your chest, which wakes you up, then you snap your head back to prove to the world what an alert, awake fellow you are. Next, you try to show that you have been following the movie by making a comment you hope is pertinent to what is happening on the screen. Her husband just died.