Best way to test that is to set a low heart rate notification to a level above your normal sleeping minimum heart rate and see if you get a notification in your sleep. Your sleep monitoring will show typical lowest heart rates.
The Apple Watch has been known to save lives, but it should not be considered a medical device, and medical supervision should be sought with specific conditions..
The article Track your sleep with Apple Watch – Apple Support does not indicate what warnings are still active during sleep.
You could reach out to Apple Support directly. You should be able to reach them here Click here > Contact - Official Apple Support or phone numbers Click here > https://support.apple.com/en-us/HT201232
and or Genius Bar Reservation and Apple Support Options - Apple