I rode my bike a long way and felt invincible. Then I rode back and realized I was riding with the wind at my back before and now I was riding into the wind. I downshifted pathetically and doggedly rode in the lowest gear. I could hardly drive back. Jell-o legs. Drippy sweat. Fie on physical fitness.
The cats have it right. Sleep all day, especially if there is sun, have an evening meal, repeat.