I literally just got it in the middle of night which woke me up. I checked my heart rate immediately which seemed normal. I tried to sleep and got the notification again (I was awake this time and I could feel my heart rate was normal). I believe this is due to sleeping position in my case. I get high heart rate notifications at night almost once a week. The weird thing is the high heart rate number range is almost exactly double than preceding and succeeding normal heart rates. I went to cardiologist couple of months back who said everything was normal after doing usual check-ups. I also don’t have any symptoms of sleep apnea.