One of my clients was confused by his laptop which would randomly come out of hibernation during the night. This could cause problems if he wished to hibernate the laptop for travelling - if the laptop were to wake itself unexpectedly it would drain the battery and pose the risk of possible overheating whilst in his luggage.
I stumbled across a very useful command line tool which allows you to see which device last caused the laptop to 'wake'.
Open Command line (Start > Run > type 'cmd' and run).
At the prompt type: powercfg -lastwake
And there you have it - it will tell you the name of the last device to wake the system from hibernation or sleep and you can then go into device manager > Power management tab and change the setting that allows the device to wake the laptop.
There are more useful tips for preventing the unexpected waking up of a machine in this article.
Now how to stop myself from waking up in the night...? Stop worrying about computers!