The part about reading but no longer comprehending sounds very familiar. If it happens twice that I’m looking at the words, but my mind is going somewhere else, I judge myself ready to fall asleep.

Then after closing my eyes I go through the stuff I just read (to avoid getting stressed out over real-life stuff), and after a while will have one or more thoughts that make no sense.

That’s the sign that falling asleep will happen very soon. From there on I don’t know what happens next.