some days and other days

Last weekend, I worked outside all day long.  I plowed through and made great progress on the patio project.

Today, I worked about 1.5 hours this morning shoveling dirt to start leveling off the brick area.  Even that was slow progress with frequent breaks.  Eventually, though, I came inside and slept for 3 hours to recover from the effort.  I just woke up again.

I wish I had a clue why some days are so different from other days.