Accuracy of Apple Watch Heart Rate Sensor? I own an Apple watch series 2 and I've recorded my heart rate during sleep for a week now. Twice during this period my heart rate during sleep shot up to around 110 for 1.5 to 2 hours and that seems very suspicious to me.
Since I don't have any sleep problems (that i know of) I was wondering whether this was an inaccuracy of the heart rate sensor.
So I wanted to know whether there is some consistent way to trick the sensor into recording double the actual heart rate (e.g. by pressing the watch against the wrist or something).
If you are concerned, you need to see a doctor.

That being said, dreaming and nightmares during normal REM sleep increase your blood pressure and heart rate. REM sleep lasts, on average, for about 20% of your total sleep time.

To calibrate your watch, you could always purchase a relatively inexpensive heart rate monitor to see if both devices sense the increase, and how accurate they are in comparison.