Determine if it failed to sleep or if it slept and subsequently awoke (and when). The System log has this information.
There are any number of things that can awaken a sleeping computer.
Thanks.
Some more detail. When I opened the computer in the morning it was on but unresponsive. Very hot, fan running, but screen black. I did a hard reboot and it booted as usual.
I'm in Israel and my system time is EST. So shutdown is about 11:30 which is 18:30 for me.
It seems to have failed to sleep. There is no log entry for the time I shut the lid. The first log entry after that is for the next morning after I hard booted.
Among the boot up log entries is an error:
The previous system shutdown at 11:24:28 AM on 5/13/2018 was unexpected.
That is roughly the time I closed the lid. So it registered a shutdown then but failed to log it at the time and also failed to power down? Or the system clock froze and it logged my hard reboot the next morning as happening the night before?