The main causes of numbness in the feet after sitting for a long time are
Sciatic numbness: in normal people, the sciatic nerve originates from the sacral plexus, passes through the pear-shaped muscle and travels towards the back of the lower limbs. When sitting, the sciatic nerve is in a state of tension, which generally does not produce numbness and abnormal sensation. However, too much time (especially unilateral exertion resulting in excessive strain on the pear-shaped muscle) can lead to excessive tension on the sciatic nerve and excessive compression by the pear-shaped muscle, resulting in abnormal sensation in the lower limbs.
Ischemic: after prolonged sitting, the blood vessels in the lower limbs are compressed, leading to ischaemia of the nerves and tissues and producing numbness.