Reading Before Sleep

I wonder how many of you often feel the dilemma I'm caught up in almost every night--the question of what to read before sleep. Nothing worse, the doctors tell us, than staring at the computer (etc.)screen before trying to fall asleep. For me, as a fiction writer, the irony stands out that nothing seems to be better--I'm not saying, really, more conducive--for preparing for sleep than reading a few pages, maybe, if you're lucky, an entire chapter, of a novel, especially a genre book, you know, a thriller or mystery or science-fiction. Feeling sleep about to descend on me (or ascend in me?) always alerts me when to stop reading, and save the clarity of winging through an exciting or explosive chapter for the next day. I wonder if a similar impulse works for writers. Hemingway said he stopped when he knew where to begin the next day. I've always used that as a working principle myself. What do you think it is--the nature of this paradox--that makes a book both exciting and soothing at the same time? What is it about a really terrific book, one of those famous page-turners, that turns us toward sleep?