system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Body Parts falling asleep; lack of oxygen or blood pressure too high?

When your leg/arm/ass/hand falls asleep and then becomes impossible to move, is that due to blood flow being cut off and so there is not oxygen, or is blood being stopped from returning to the heart so pressure builds up and nothing can move (like a garden hose with really high pressure, hard to bend)?
Follow up question: when blood flow is returned and we get that "staticy" feeling, is that oxygen returning to nervous system cells so feeling is regained?
gpt
>lack of oxygen or blood pressure too high?

Neither.

It's caused by compression of nerves to/from the affected limb, effectively cutting off communication between the limb and the brain.  The "pins and needles" feeling is caused by the sensory neurons restoring their electrochemical gradients once the pressure is removed.