I had wide-awake nightmares as a child. I was in that sweet spot between awake and asleep and would hallucinate creatures in my bedroom that obviously were not there. I can still see some of them in my mind to this day. Most of them were innocent enough like Kermit the Frog or something like that, but obviously they were not actually there. I grew out of that around 10 years of age but for a while there I was afraid to go to sleep at night.
That must feel terrible at that young age.
It's not linked to your situation but I don't allow my kids to watch creepy or horror cartoons. Whenever they do, they always get scared in their sleep or whenever they are alone they fear monsters will come and eat them. 🫠 It's annoying when they get extra clingy for no reason. But yeah sometimes it is serious and you need to listen and counsel them to help them out of the situation.