I have been struggling with this very same thing over the past week or so. I haven't changed eating, workouts, or sleep, but it feels like a huge effort to even put one foot in front of the other or to pick something up. Definitely a difference from my previous energy level.
Right now I am chalking it up to the heat but you have a good idea; I should go take my blood pressure. If it's still going on next week, I will see the doc and see if maybe my iron is low. I'm not sleepy, just have no energy in my muscles. It's puzzling.
And now that you don't have to be perfect, you can be good.