I would check to make sure that the tail drive belt isn't slipping on the front gear.....that would make it spin. Also, if you have it set up to where you can remotely alter the gain settings on the controller, you might want to make sure that it didn't accidentally get switched out of heading hold mode.

It definitely looks just like a reversed gyro though.

When you move your rudder stick to the right, the tail pitch servo should pull the push rod towards the front of the heli, and if you hold the heli (throttle hold on) with the nose pointing at you, and rotate the heli to your left, the tail slider should go towards the boom, and the servo should pull towards the front of the heli.

If your gyro is pushing the tail slider in the wrong direction, then you need to reverse the gyro. If the rudder stick is pushing the slider in the wrong direction, then you need to reverse your rudder channel on your receiver.