Your legs are wobbly, your chest is hurting, and you can't breathe, which is probably a good thing because it keeps you from screaming and squealing like a teenage girl at a Beatles concert.
That's what it's like watching Usain Bolt. You can't allow yourself to blink, either, because in the time that your eyelids go all the way down and then bounce back up, Bolt has moved too far, and you've missed it.
He did it again Sunday, winning the gold medal in the 100 meters, this time in an Olympic record 9.63 seconds. Bolt and Carl Lewis are the only men to win back-to-back Olympic 100s. And Bolt says he looks forward to the Rio Games in 2016.
"I've showed that without a doubt, I'm the best,'' Bolt said. "This is where I want to become a legend, and that's just one step in the door.''
Too late for that. Bolt is already a worldwide legend. He is, and already was, the rock star of these games. No offense to Michael Phelps, but even his swimming records were a warm-up act for Bolt.