I've had this happen before. I do have PTSD so I get flashbacks. But I have experienced what you described...between wake and sleep. I think it's normal and there is a name for it. Ask your doc if it bothers you.

I get this regularly and I can recognize it when it occurs to me I'm technically still awake but my thoughts are moving freely on their own. Right before I fall asleep.

That said, it doesn't happen when I'm manic because I tend to not sleep during mania.

I don't know if that helped?