When we exert willpower or mental effort, it uses up glucose from the blood in the brain. One way you could explain the exhaustion that comes from using magic is that it requires mental effort to the point of creating dangerously low levels of blood sugar in the brain.
When we exert willpower or mental effort, it uses up glucose from the blood in the brain. One way you could explain the exhaustion that comes from using magic is that it requires mental effort to the point of creating dangerously low levels of blood sugar in the brain.