Defense Against Dualism

How do you account for the fact that consciousness is also relative to the motion of the brain? An astronaut going many times faster relative to us would be thinking as fast as us subjectively, but when comparing from our motions relative to each other, we are the ones thinking quite faster, since time is slower for the astronaut. If our mind is detached from the physical world, how come the astronaut doesn't think much slower than we do?