Roll onto your arm in your sleep and you’ll likely wake up to find it numb and lifeless, as if it wants to sleep in. Then comes the sensation of pins and needles. Contrary to what you might think, limbs don’t go limp simply because you cut off their blood supply when you lie on them wrong. Instead, you’re pressing on nerves and cutting off the limb’s communication with the brain. Roll off and the nerves go through a sort of ‘’reboot,’’ sending pulses to the brain that you perceive as that tingly feeling. The lazy limb comes back online in short order.
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