Those back scratches are from a diferencia galaxy.

Not fun for the cat. If it purrs, great. If it acts like this, it’s not pleasurable. “A cat’s tail is a 12″ (30.5-cm) extension of its highly-sensitive nervous system (spine), plotting tons of nerve endings in one small cluster near the tail’s base. Long or aggressive scratches can trigger a pain or stress response in these sensitive nerve receptors.”

Hyperesthesia syndrome?

I've recently been doing this to my cat as she has a similar but not so audible response,, the out of control head movements, the random mouth biting and total lose of composure whilst i scratched her there made everyone who saw laugh.. then i started thinking about it.. its a highly sensitive zone and the feeling is obviously overwhelming.. i don't purposely do it like in the video anymore as I'm afraid its turning an act of wanting my cat to be happy into her being over stimulated, plus the other day i woke up to her biting the area and what i thought might have been fleas or an irritation was some sort of skin rash that had dried, i carefully washed the are with a warm washcloth and have been keeping any eye on it for the past few days...

has anyone else had a problem like this? like the cat has scratched itself to the point of a scab forming then it self healing and falling off at the mere scratch with fingernails?

I mean doing that do any cat will overstimulate him, or make him horny.

Why would you do that.

Almost certainly has a skin condition. Does not look healthy.