Are you in really good shape?
I'd read a story about an older gentleman in Australia who had been athletic all his life, had a resting HR in the low 30's or high 20's, but when he slept, his average HR was 18, and he had episodes where his heart would also stop from 3-9 seconds at a time.
He needed some intervention, but ultimately was fine, continued to run marathons, and claimed that since he was getting better sleep, his running times were improving.
Best of luck with your tests.
I am happy you are getting medical treatment/testing. I do not have any conscious knowledge of heart pauses, but I do have an irregular beat, due to AFib. I can't immagine a lapse of 9 seconds, I take your post to say no pulses for 9 seconds. I'd think that would "knock one out" if they were not asleep, but you are proof that sleeping is relaxed enough to just let it pass. You didn't say anything about the pause waking you up.
Sorry, not trying to scare, you are already nervous. I read you post to say even with a monitor on there were no long lapses in your pulse when you were awake.
A sleep study will tell if there is anything else unusual going on while you're asleep, I assume, I have no knowledge of what a sleep study is other than I believe it includes monitoring of your breathing and brain activity (electrical) as well as you heart functions. Maybe that will pull everything together in a way that a treatment/fix can be prescribed.
Good luck, let us know how it all goes.