Still tired today

My wakeup heart rate was 53 again. I felt a little bit better than I did yesterday, but I was still tired during my run. I thus cut the run short again, doing 4 miles. I've been sleeping well, and that is a very good sign. I just have to give my body some time to recover from my run on Saturday, from the high heat, and from the higher relative humidity. It was in the 70s (F) when I ran yesterday, but in the afternoon the sun came out and it got really hot.