Worst Workout Ever

I had one of the worst workouts ever today. I went out for a jog at around 4pm once I finally decided it didn't look like it was going to rain anymore today. It was very humid and not too warm, but much warmer than the cool 6am air I am used to. I don't know what happened to me, but about 15 minutes in I just couldn't jog anymore so I walked for a minute, then tried to jog again. I kept having to stop and then just gave up and walked the rest of the way. My body just had nothing left in it and I have no idea why. When I got home I was completely exhausted. I just sat on the couch, then took a shower and took a nap because I was too tired to do anything else. Now at 9pm I am finally feeling better, but it was really odd. I hope this doesn't happen again.