Goldberg says he's seen many people end up in the ER because they've failed to respond to that weird prickly feeling, perhaps because they've been knocked out by alcohol, sleeping pills or a punch in the face. He explains that when you've been kneeling for too long (or doing something else that puts pressure on your leg), the arteries in that area can become compressed, preventing them from providing tissues and nerves with oxygen and glucose. This also blocks nerve pathways, causing some nerves to stop firing and others to go off like a 4th of July fireworks finale. When the brain receives these signals, it interprets them as that uncomfortable sensation of pins and needles. Prolonged pressure on the arteries can indeed lead to temporary or even permanent nerve damage, so it's important to respond to the feeling as soon as you notice it.
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