I went out for a 5K run. I jogged for 5 minutes as a warm-up. Then started running. After about 2.5 kilometers, I got really tired and had to stop. So I then walked for about 1 kilometer. Then I started running again, and, weirdly enough, I was now running way faster and with way more energy than I did for the first 2.5 kilometers.
What happened here? How come I was FASTER during the 2nd stint?