My wakeup heart rate (WHR) was down to 55 this morning. It has been around 61, and that decrease is significant, especially with the 7 mile run I did yesterday. That run was more stressful than it would have been due to the big hill in the middle of the run.
I've learned from experience that getting sufficient sleep is critical to my having a low WHR. For most of my adult life I've felt that 7 hours sleep per night was sufficient for my body. But, as I'm getting older I'm finding that 7 1/2 hours is a good amount for me. Last night I got 9 hours.