Definitely make sure all of your programs are closed.. Maybe the browser was refreshing all night? But, I personally dont think that drop in battery life is that bad, it was on all night. Were you in an area with bad coverage?
When "closing" a program, are you escaping out or are you exiting? Press the ALT and escape key at the same time. A dialog box will appear. Release the escape key. Scroll through the dialog box and the only programs that should show up is: Homescreen, Browser, BlackBerry Messenger, Phone Messages.
If you don't properly close out of all other programs, they will continue to run in the background.