Juddering cursor

Last night I was online when suddenly my cursor started juddering. It doesn't jump around the screen, it just judders, enough to make it really difficult to click on anything. I've tried disconnecting the mouse, which is a USB wired mouse, but even when the mouse is disconnected it still judders.

I've restarted the computer, but it's still happening.
Please does anyone have any ideas as it's driving me crazy!