My cat grew an enoumous lump near her neck in the very middle of her back. About two thirds of it is pushing up into the skin and the rest is clearly pushing in on her. Its abnormally shaped (peaks an vallys are the only way to describe it, kinda lumpy) and firm on most parts and soft on other parts. It moves from side to side freely, but not up and down. It doesn't sppear to be attached to anything but the skin, possibly part of the back. It grew seemingly overnight, I didn't notice it coming it so it must have grown quickly. It's getting slightly bigger I think. What do you think it is?