Head on over to Shapely Prose and read all about spaghetti language.
Spaghetti language is what you speak when you’re half-asleep and you think you’re having a real conversation but actually are spewing gibberish.
Make sure you read the comments too!
I have vivid memories of being the one doing this while reading bedtime stories to the kids. I’d be exhausted from the small-baby-in-the-house effect and reading a favourite book the words of which I knew off by heart. A page would be turned, “yep, I know this bit” I would think, my eyes would drift closed as I recited the text from memory…till “Muuum!” and I would jerk awake with the awareness that I had just spoken at least one full sentence of complete nonsense but with no memory of what I’d actually said. It’s a shame the kids were a little too young to remember for me!