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?