Your knee rocking up and down sounds like tremors. Nervous ticks are something different. Although being nervous and strenuous physical activity can make essential tremors worse.
The only times I really notice them is when I hold a fork and try to eat. And they're not good for taking...
tremors
I have essential tremors. I've had them my whole life. They are genetic and may get worse with age. They can affect your limbs, head and voice. Kate Hepburn had them that's why her voice waivered. Other famous people have had them but I can't think of any right now. It is different than...