system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it painful to move your leg after it goes numb?
gpt
I assume you're referring to the pins and needles feeling? 

Your foot "falling asleep" results in pressure being put on different nerves or blood vessels so electrical impulses/nutrients and oxygen can't be sent to the limb. So when you adjust your position and relieve that pressure, the nerves start to function again. But it's like rebooting a computer, it doesn't all happen at once, so the pressure receptors and pain receptors go a little crazy for a few minutes until chemical equilibrium is restored. Just wiggle your toes to get the fluids pumping and will be over soon.