Even though my wakeup HR was 50, I felt tired during the run; I considered aborting the run but decided to finish. I ran Monday evening and then Wednesday morning. So, I had less rest after the Monday run than I usually have when I go from Monday morning to Wednesday morning. I've been consistent during the past week of getting 7 hours sleep, although last night I got about 6 3/4 hours. I don't think sleep was the cause of my being tired. It's natural to have ups and downs in how a runner feels, and I may be in a slight dip.