What is meant by “He lived a year in a minute”?

Rainsford is being persued by the evil General Zaroff. Rainsford is thinking that"He lived a year in a minute" because his body was so full of adrenaline, his "fight of flight" response was working in overdrive. The fact that he was being hunted, and could die at his first mistake, made Rainsford feel like one minute (as prey) feel the same as if he had lived a whole year doing what he usually did.