I was a slowpoke today

I am not sure what caused it, but I was unable to keep a constant speed. I rode for 1 hour and six minutes and covered 15.15 miles at an average speed of 13.8 mph and a max speed of 23.5 mph. I just felt weak and unable to have what I feel is a normal ride which means not killing myself. The weather was nice with a temperature of 72 degrees and the wind from the West at 8-15 mph, but the gusts seemed much stronger.