Has anyone experienced high bmp during sleep ?

In my reading and my own experience (using a Galaxy watch), this is almost certain, not absolutely certain, to be attributable to one of two conditions:
a. Sleep apnea - where your heart has to race to keep you alive because your serum O2 levels drop when you cannot get air past your pharyngeal tissues and nasal tissues, or past your upper trachea; or
b. Dreams....REM sleep stage. When we dream, all sorts of unknown/unseen things happen, from sexual stimulation/arousal, to thrashing, to calling out, to swinging wildly, to vocalizing, and feeling terror or joy. If the dream is quite vivid, and would otherwise cause waking arousal of any kind, stimulation, then the body treats it the same way...increased respiration and heart rate, adrenalin production, increase in serum cortisol, etc.

Welcome to Connect, @lbt . Your concern about your rate tracked by your Apple Watch during sleep is valid, especially since you notice it only recently.

@gloaming has offered good information already. You mention having an upcoming appointment scheduled with a new cardiologist. If you are comfortable, it may help others know how to comment if you share more about what health conditions you have and why you have been seeing a cardiologist.

I am including information about heart rate that may be useful to review. The entire article is valuable, though I want to point out scrolling down to see a section about how your heart rate changes during sleep. In part, if your heart rate ‘continues to stay elevated or is accompanied by symptoms like chest pain, heart palpitations, or difficulty breathing, it’s important to consult a healthcare provider.’
-Normal Sleeping Heart Rate https://www.sleepfoundation.org/physical-health/sleeping-heart-rate

It may put your mind at ease a bit to call your new cardiology office and ask them if you could come in sooner if they have a cancellation. Do you have symptoms in addition to your recent change in heart rate? Has anything else changed with your lifestyle, medications, etc. in this same timeframe?

@gloaming thanks very much, I will be mindful to check if the high rate might be connected to any unusual dreaming
I started to do some research but was not aware of that connection

@jlharsh thanks for all the info, I appreciate the article as I did not come across this one during my research. As for additional info I am a female age 63 and see a cardiologist annually for family history (grandfather and uncle had widow maker heart attacks early ages) I myself have an enlarged heart
My annual visit would be in June and not being established in my new location the earliest I can find an appointment so far is April. I am working on being seen sooner. As for medical conditions I am a cancer survivor, high cholesterol (on a low statin) as well as talking Levothyroxine for thyroid (had hemi thyroidectomy) some anxiety but physically active