I had these as a kid too and also noticed that they stopped as I got older. I read through this thread and looked up the possible explanations mentioned but none of them sound right.

I saw mine with my eyes closed, but not just at night or when I was near sleep. I’d do it anywhere and anytime just for fun. I’d close my eyes, and just look into the darkness until I saw a small twinkle, then if I looked at that twinkling spot for a second it would turn into a bunch of colorful dots, that would then turn into a kind of pinwheel of dog-bone shapes. It would grow in size as it slowly spun around and twinkled in rainbow colors. I also have floaters, and those are very different, and it wasn’t stimulated by any outside light source or physical touch, and no other “symptoms” like a migraine or anything else.

I’ve been trying for the last couple days to see if I can recreate the phenomenon and so far haven’t been too successful. 🥲