fall asleep while reading

I read a lot of books every year. During the day when I sit or lie down resting on the couch, and at night in bed before I go to sleep. Now, I’m often so tired that I accidentally fall asleep while reading. And then something strange happens: my thoughts continue seamlessly with the story I was reading, but this continuation is created on the spot by my subconscious. When I wake up again, I find myself in two different story lines at the same time, and I have to look for the last lines in the book that I actually read, so that I can pick up the story of the book again. This sometimes happens up to five times within half an hour. I wish I could draw on that rich imagination – which fits in seamlessly with what I just read, but in the meantime goes its own way – in my full consciousness. Unfortunately, those fabrications disappear without a trace a few seconds after I wake up.