After Windows Update performs an update for your computer, it usually prompts you to restart. You might accidentally hit restart and all your unsaved work gets lost.
The way to stop Windows Update from nagging you to restart is to end the Windows Update service until next time your computer starts. This is done with or without the command prompt like so:
Without command prompt:
Go to Start > Run, type net stop wuauserv and press [Enter].
With command prompt:
Go to Start > Run, type cmd and press [Enter].
In the command prompt, type sc stop wuauserv and press [Enter].