Sometimes, in the middle of grooming, my cat goes crazy and starts to bite his hind legs ankle and also kicks under his chin with his legs, for no obvious reason. And he wiggles so erratically that he almost topples my monitor if I don't interfere.
This happens only when he is at an arms length and I'm watching him. I've never seen he does it when he is grooming away from me.
He exhibits this strange behavior is recently much more frequent.
Apart from that, he is a gentle and wise 5 years old ginger tabby European cat. I've adopted him at the age of 2.5 from a shelter and I know nothing about his early life.
I'm wondering what might cause this behavior, and how to deal with it?