Feel like I'm blacking out when falling asleep?

This happened 3 times last night, I had woken up but was still very tired so I kept my eyes closed. While they were closed I was getting this split second 'flash' of extreme darkness, like unplugging a computer. Felt like a blackout but I was still conscious and it I'm not sure if it's just a hypnic jerk because I was still tired and wanted to go back to sleep (I see bright white flashes sometimes while trying to sleep, this was like a flash of extreme black)

I've been having palpitations recently and I keep worrying these are blackouts due to my heart :( I havent experienced any while awake quite yet, I'm dreading feeling one if it happens.
I'm so stressed about this.

Have you ever been diagnosed with sleep paralysis?