I woke up after 6 1/2 hours sleep. I knew I wouldn't go back to sleep, so I got up and measured my wakeup HR -- it was 50. I did some things for an hour and then went back to sleep and got 30 - 45 minutes of additional sleep. When I got back up, my wakeup HR was 47. I've noticed that pattern on several occasions. I get up for a while and then go back to bed for more sleep, and my wakeup HR drops significantly. Sleep deficit really does affect our bodies!
During the past week or so, my wakeup HR has been in the high 40s. This is a good sign that my body is becoming stronger as I do longer distances. I hope this trend continues. When I ran marathons 24 years ago, my HR was 44 for a year or so and then 40 for the rest of my marathon experience.