I wore my HRM last night as I slept to see if I'd find anything interesting. Well, my average throughout the night was 42 BPM. I had two dips into the low 30s and several spikes throughout the night to around 70 BPM. I want to wear it again and see if I get consistent results. I thought it was interesting that near the end of my sleep my HR rose to 50, then 70, then it was wakeup time. I don't know if I was sleeping still at 50, but I think 70 was right when I woke up and it didn't go back down. I think the alarm clock actually made my HR rise.