(Rhetorical question. I'm pretty sure what happened.)
Last night I set the computer to "Hibernate" mode and got to bed early, which I'd planned and hoped to do. Dreams occurred, so I know I was indeed sleeping -- I'd somehow been roped into appearing in a version of Saturday Night Live that was being recorded in someone's basement, and I was in the room serving as a set thinking both Wait a minute, I suck at improvisation and Whoa, people I know on the Internet are freaking out about me being on the show! -- but then in the 4 o'clock hour I awoke to hear the computer. I turned my head and saw some of the computer lights, though (thank goodness) not the monitor, on. I got up and turned on the monitor, and saw that the computer had restarted. Not what I'd wanted to do last night, but apparently at that point the computer was ready to install updates. And had been running for hours, waiting to be used again, when I do try to shut it off overnight.
(I say "thank goodness not the monitor" because that would've meant more light in my room. Occasionally I've fallen asleep with my bedside lamp on, and when I do that, my sleep is never deep enough. I wake up especially out of sorts. The monitor being on may have had a similar effect, the equivalent of poking at me and going "You're not quite asleep, right? Not really asleep, yeah?")
What annoyed me was, I'd been setting the computer to "Hibernate" so I could keep certain web pages up. The restart in the middle of the night closed all of those tabs. (I say "all," though there weren't many, not the number of tabs Neil Gaiman or yendi are known to have open on their computers, but again, they were open on my desktop for a reason.) I can dig them up and re-open them; I just don't want to, because I shouldn't have to.
Before I decided that the computer most likely restarted -- that maybe I'd accidentally clicked "Restart" instead of "Hibernate," say -- I pondered. Plus in the 4 o'clock hour I wasn't THAT rested considering when I'd gone to bed, so my pondering could go in odder directions than it even usually does. Maybe I woke up at maybe 1:00 or 2:00 and got back online, I thought. I wasn't sleep-walking, I was sleep-surfing.
Prrrrrrrrrrrrrobably not. But the idea of sleep-surfing slightly amuses me.