What causes pins and needles when your leg falls asleep?

When your leg falls asleep, it’s because you’ve put pressure on a nerve, which blocks its ability to send signals to your brain^[1][6]. Once you move and release that pressure, the nerves suddenly reboot and fire off a flood of disorganized signals, which your brain interprets as that classic pins and needles sensation^[2][5].

Commonly, people think this is just about blood flow, but it’s actually a mix of both nerve compression and restricted blood supply^[5]. Did you know that hitting your funny bone is actually just you smacking your ulnar nerve^[1]?