Heart racing when falling asleep

20F, 147lb, no medical history, taking Vitamin D 5000 IU daily

I take naps in the afternoon during days I have early morning shifts, usually for an hour, but for the past few weeks, right before I drift off to sleep my heart races like crazy. It felt like my entire body was trembling before I realized it was my heart. It doesn’t disrupt my sleep much, after it calms down I fall asleep easily, but it’s been freaking me out and I’m not sure what’s causing it. I read that it might be related to anxiety or stress, that might be the case since I’ve been studying for finals, but even before this it still happened but just not as often.

I’ve also had a similar thing happen where I’m already actively sleeping, but then have a mini dream of tripping on something that jolts me awake with my heart racing. It hasn’t happened in a while, now it’s just this heart racing before falling asleep. Is this something serious? It isn’t really disrupting my sleep just a bit scary