Odd spike in HR while sleeping

I have been using my Apple Watch while sleeping in combination with a sleep tracker app to monitor my sleep patterns. I have had heart related issues in the past but it is not cronic and the Cardiologist has more or less given me a clean bill with some minor medications and instructions to keep an eye out for symptoms. Part of the reason I like the AW.

I have gotten errant readings from the AW HR Monitor before but they usually quickly correct back to normal. Last few nights I have worn my watch while sleeping and pulse settles in to about 65 bpm after falling asleep and stays there till I wake. Normal so okay... Last night started out similar fell asleep around midnight and settled in to around 65 bpm but then around 3:30am My heart rate spiked to 120 according to the AW and then bounced between 120 and 130 till 7:50am. It is possible that this is accurate, but I wanna say unlikely as my wife said that I was sleeping very soundly, no snoring no restlessness and both before I went to bed and when I woke up my HR was around 75 and my BP 90/60 according to my BP monitor so.... I am wondering what could cause a false 5 hour spike in my HR reading. Maybe I was laying on the watch or something. I am gonna check in with the doc to be on the safe side but I don't want to use something that is gonna cause me to falsely think I may have a serious issue all the time.