I've recently been experiencing on my SGS II that it shuts itself down in the night (usually at similar hours). I have also done some research in this matter and found out that this was also plaguing the previous Galaxy phone. I have the latest KWE7 update and i'm pretty sure it didn't happen before that. Could it be some app that is causing this? I really can't be bothered to reset to factory settings - AGAIN - or to uninstall all my apps so I thought i'd ask around here if anyone else is having similar problems.

Had the same problem, install a app called Load Monitor, once installed go to settings and setting "Auto start" to on and a setting called "Wake lock".

If this doesn't get the job done, also install "Advanced task killer", this kills not needed app when the load gets to high.

The phone shuts off because of to high ~loading levels~ or what ever.

Let me know if it did the job for you!