I've been having this problem for a while now, I come back to my PC which should be asleep and it's completely off.
Upon boot I'm asked about starting in safe mode etc, making me think it's an unexpected shutdown.
Looking at the error logs I find:
Error 41, kernel-power - the system has rebooted without cleanly shutting down first.
6 times this month already..
any suggestions on troubleshooting the source of this?