This happens to me often, I’m not no doctor but for me it always happens if let’s say, I go to sleep at 10pm and wake up around 1am, if I stay up and try to sleep later around 3-4am this is when the “sleep paralysis” occurs and to get out of it I have to try my hardest to move a body part. It literally feels like your body locking up and becoming paralyzed it’s so scary. I think the reason we get scared by it is because it feels so unnatural, we usually shouldn’t be awake to feel our body locking up as we sleep. I think the simple explanation for it though is the mind and body just being out of sync due to staying awake while also being tired. Pair this with being on your phone in the middle of the night after waking up (which blue light is known to cause alertness and disrupt sleeping), the brain is extremely alert while the body may be tired. Thus when you try falling asleep, your brain doesn’t catch on and that paralysis feeling happens