system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does the loss of blood result in the 'pins and needles' sensation?
gpt
It doesn't. A limb falling asleep isn't caused by a loss of blood flow. It's caused by pressure being applied to a nerve, causing it to stop working. So signals don't make it from that limb to your brain. 

When the pressure is relieved, the nerve can start sending random signals as it gets back into equilibrium, which you perceive as the "pins and needles" sensation.