Originally Posted by Eagle

Most likely you were doing some very hard braking, stopped the car put your parking brake up or had your foot on the brake pedal for a long time while at a light or something.
This is enough to cause your pads to melt, which creates excessive "pad deposits" on your rotors. The absolute sure fire fix is to change your pads and resurface your rotors, doing some hard braking or a brake pad bedding procedure may or may not help.

It's highly unlikely you actually warped the rotor.