I did 2.0 miles with my wife

My wife and I were out about 9 am and went north from 100th South on the Parkway. I did fine for about 3/4 mile, and then I started to run out of energy. My legs felt fine, but my body was really tired. In fact, I walked most of the mile back to our car. The temperature during our run was in the high 70s (F) and low 80s, warmer than last Saturday but still better than the 90s during mid-day. I only had 6 hours sleep last night, better than the 5-5.5 hours I've been getting but not as good as the 7 hours I need. I'm hoping to take a nap later today.