Weird display problem -- cause?

Ack. Should've taken screenshots. But it's solved already and I was just wondering if it has also happened to others, too. And more importantly, what caused it.

For the first time since the day I received my laptop, I've been running my Vostro on AC power. Now, I booted up on battery and the weirdest thing happened.

My welcome screen was all big and distorted. So I logged in and then right click the desktop then Properties. There it was, my resolution was at 640x480 and the color quality at 4-bit. And I couldn't change it.

Then I went to RivaTuner, thinking it could be a driver problem. Strangest thing. Across the filename "nv4_disp.dll" [description: display driver], the version was 56! [actually 56 point something, but yeah I didn't take screenshots and...]

I went right into reinstalling ForceWare 169.04. Ta-da, done. Problem solved.

This really had me panicking because I knew and expected PowerMizer to do something to my display [lessen screen brightness] to save on battery life, but I never expected that. Somehow, I think the driver killed itself. [I also wasn't sure whether to post here or in the graphics/gaming section]

So has this also happened to anyone? What could've caused this problem? If it helps, I do not overclock and, again, this has only happened to me now and it happened for the first time I'm using this on battery power with 169.04 installed [or at least, supposed to have been installed]. The last time I used this on battery power was the first day I had this laptop and it was on stock display drivers.

Thanks for your time!