I ran 8 miles in the late afternoon, but I was tired, even though my wakeup HR was 52.
My wife and I had a breakfast date, and I, of course, ate too much. I went out running 4 hours later, and I could tell as soon as I started that I was short of wind. After I warmed up, I did better in my breathing. My lack of energy during the run may have been due to my lack of sleep earlier in the week (it's common for lack of sleep to take more days for recovery than the days with insufficient sleep) or my run yesterday -- my body isn't used to running two days in a row.