Hibernate in windows 8.1

looking at the power options in control panel on my laptop, the word " hibernate" does not appear, instead the word " sleep" is predominant. However when I leave the laptop overnight or for a long period, it hibernate, why?

Are you sure that it is hibernating not shutting down?

Usually once the laptop detects that the battery is about to run out, it will come out of sleep (standby), and save the contents of the memory to disk (hibernate), so that if the laptop battery does indeed run out, once it is brought back to life it can still recover the state it was in.

It is not shutting down. When I shut the laptop down it takes much longer for the desktop to appear.When I close the lid and lift shortly afterwards, the desktop appear instantly, presumably from sleep. When I close the lid and open it the following morning, it takes longer for the desktop to come up, the dell logo comes up first, then windows caption with the rotating dots!!, then the desktop, I assume it is coming back from hibernation. In fact sometimes when it comes back from hibernation, I get a black screen, so I resort to closing the lid for few seconds and when I lift the lid I get the desktop!! very strange.

In reply to a post by samulam:

It is not shutting down. When I shut the laptop down it takes much longer for the desktop to appear.When I close the lid and lift shortly afterwards, the desktop appear instantly, presumably from sleep. When I close the lid and open it the following morning, it takes longer for the desktop to come up, the dell logo comes up first, then windows caption with the rotating dots!!, then the desktop, I assume it is coming back from hibernation. In fact sometimes when it comes back from hibernation, I get a black screen, so I resort to closing the lid for few seconds and when I lift the lid I get the desktop!! very strange.

See my reply - it is probably to do with that. Check power options for something like "Hibernate after x hours" try disabling it - this may still be taking effect even if laptop is in sleep.