Ahh,I’ve been wondering if others experience this too!! I began a few searches but never really found much, and I’m kind of unsure how to even search properly for it.
For me, it happens as I’m laying still, slowly waking up and usually when I still feel fairly sleepy before fully waking up. A series of flashing images, more like bright lights really, in such fast succession and mostly in geometric forms, various colours.
Sometimes, though, it’s just one bright flash that peaks in brightness before disappearing.
I’ve noticed something distinct about the experience though: once it’s done, I’m 100% fully aware and alert. It almost feels like the full stop at the end of my sleeping/dreaming journey, kind of similar to the way a shamanic drum journey ends with a faster, more intense rhythm (which, without fail, brings one back to a fully awake state). It’s not ever really linked to the end of a dream, not even the dream state, but more so the end of a sleepy state.