I've recently noticed this myself aswell, reason being that I got a new tv. I kept my sensivity on 8, but it felt so weird.
I also had problems with 180 or 360's.
I decided to get my aim back by killing bots (regular) in Black Ops. Each day I made some progress and after a few days my aim was back

Maybe you can do the same or is it just something with your settings / controller.
Goodluck!