Have you tried using Standby/Suspend?
I always use that, and when it feels like it it will hibernate in the middle of the night - probably if the battery is getting down but I don't think I've found any correlation between when it stays suspended to when it wakes and hibernates.
Anyway, try suspend.
edit: actually, it's called Sleep on Windows.
EDITED: 30 Sep 2014 14:00 by ANT_THOMAS