Is it dangerous when your leg falls asleep?

Dear Cecil:

After enjoying a lazy Sunday-evening game of Trivial Pursuit with my sweetie, I learned that one of her feet had fallen asleep under the coffee table. Wondering aloud what caused this, we decided it was a feedback device for self-protection. However, nobody ever told us if limb snoozing can be dangerous. Can your arms or legs sleep so soundly that damage occurs?

Cecil replies:

Dear S.:

Trivial Pursuit–let me tell you, there’s the story of my life. Anyway, forget that “feedback device for self-protection” stuff. The numbness you’re talking about is called neurapraxia, and it usually occurs when some major nerve gets compressed between a bone and some other hard object, such as a table or another bone. Nerves that are particularly vulnerable to this include the ulnar nerve, which runs through the funny-bone channel in your elbow, and the peroneal nerve, which runs through a similar channel at the top of the fibula near the knee.

Fortunately, the blood continues to flow normally when your limbs fall asleep, so it’s not like you’re going to get gangrene or anything. There are two possible dangers, though: first, if you put weight on a numbed-out limb, it may collapse under you, resulting in a sprain or worse. Second, if the compression of the nerve continues for an unusually long time, or if the nerve is pressed against something sharp, like the edge of a desk, a pinched nerve may result, in which case it may take days or weeks to recover normal sensation. So exercise a little caution.

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