I struggle a lot with that kind of thing too. I sometimes just have the thought that "what if theres a fire while I'm asleep and I die?" Or something like that. I almost always sleep with music playing so I don't hear my heart beat much, but on occasion I have had similar experiences. You're definitely not the only one. I hope that's some comfort for you. I've found for me the music playing can help calm intrusive or anxious thoughts that overwhelm me at night.

It's really hard to have anxiety about things that are completely out of your control.

I used to have a similar issue! I would stay up at night worrying about my irregular heartbeat. I don’t fully remember how I separated from the anxiety of it, I’m sorry. But do know it is possible, and I believe you can do it :)