The numbness of the hands and feet is a kind of abnormal feeling. When you sit cross-legged for too long, or the posture is pressed to a certain nerve, the blood flow of the nerves decreases, and the limbs begin to numb.
The nerve cells constantly send signals to the body, and each time a signal is sent, the cells need to be reset to meet the next signal. In the absence of blood, nerve cells cannot be reset smoothly, so the cells transmit signals only in terms of their capabilities, and abnormal information is sent to the brain.
When the upstream nerve cells are abnormal, the cells waiting for the signal to be received downstream will also be affected, and the signal will be sent without warning. This is what our body feels is the feeling of tingling.