If it is not possible to hold one's breath until one expires, then the "will" to live is not willful at all, but is a bodily reaction (at least in that isolated case). Furthermore, the emotions and thoughts accompanying such a reaction cannot be called willful either. A person will innevitably feel that they want to live, and will have thoughts about trying to stay alive, once their body has begun to struggle for air.
So, this is an example of a motive to stay alive, and thoughts and feelings about staying alive, that do not result from decision. The motivation, mood and thoughts all result from the body's lack of air, not from choice. And since at least once situation can be explained this way, why not assume that the rest of our thoughts, feelings and actions can be explained this way as well? The idea of 'choice' need never be invented to explain human behavior. It is a tempting idea, like God, but unnecessary.