I may have spoken too soon, as after having put it to sleep last night, this morning when I woke the PC, it was in a rebooted state, asking me to log on.
Now there is one (to me) curious aspect to this: how can a PC reboot itself while it is sleeping? I don't hear any noise whatsoever... No fans, no disks, nothing. Or does it happen while it's pretending to go to sleep? Granted, the time it is taking to go to sleep has gotten longer in recent weeks, and it can take from 30 sec up to a minute.
Here is the second curious thing. When I checked the Reliability Monitor this morning, it told me I had 27 Microsoft .NET Framework 4.5 updates, security updates, and application reconfigurations between 03:08 and 03:25. Now, both me and my PC were fast asleep then. So, how could it have been doing all these installations during that time? Could it be then Microsoft that has rebooted my machine overnight to finish the update?
If so, I'd really like to (un)check some box somewhere to make it ask me first before it reboots my PC...