Thanks to staying up too late, my wakeup HR has gone up. It was 51. My normal sleep is 7 hours. If I get 5-5 1/2 hours, my HR shoots up. Some of this might be due to my age, but I had the same pattern 21 years ago when I ran marathons. It would be interesting to see similar data from people in each decade of age, from say 20 up to the 80s or 90s.