We’ve all been there: the movie ends; the lights come up; you shift in your seat, only to find your entire left calf is missing. Or at least, it feels that way – it’s still there when you check, but you can’t feel it, and it’s certainly not doing what you’re telling it. What’s going on? Are you dying?
Worry not. A “dead” or “asleep” arm or leg is completely normal – and it’s all down to a traffic jam in your nervous system.
Why do limbs “fall asleep”?
The reason your arms, legs, hands, or feet go numb every so often is simple: it’s your nerves.
That makes sense, right? You’ve lost feeling; it’s caused by something going wrong with your feeling organs. But you may have heard something else as the cause: “Some people mistakenly think a lack of blood flow causes this feeling,” wrote Zachary Gillen, Assistant Professor of Exercise Physiology at Mississippi State University, in a 2021 article for The Conversation.
“They imagine the ‘asleep’ feeling happens when your blood, which carries nutrients all over your body, is unable to get to your foot,” he explained. “But that’s not right.”
Instead, the weird numb feeling you get – the technical term is paresthesia – is from nerves getting squished, probably from how you’re positioned. You can think of it like stepping on a hosepipe, except that instead of water flowing through, it’s information about what your body is feeling.
“Every time you decide to move your body, whether it’s standing up, walking around or playing sports, your brain sends signals to your muscles to make sure they move correctly,” explained Gillen. “When the brain is unable to talk with a muscle or groups of muscles, some weird things can happen – including that part of your body getting that weird falling-asleep sensation.”
But numbness isn’t the only symptom of a sleeping or “dead” limb – so what causes that more extreme phenomenon, where your body just straight-up decides to no longer work?
Well, whether it’s fully paralyzed or all floppy, this is still just a sign that your nerves are unhappy. Too much compression on a nerve can lead to paralysis, for the same reason that it makes you numb – no signals are getting through.
And as for the tingly, uncomfortable “pins and needles” feeling that comes when you finally shift position? That is, as strange as it sounds, a good sign that you’ve fixed the problem.
“When the blockage [to the nerve] is removed, the nerve cells begin waking up as they start receiving impulses again,” explains the University of Rochester Medical Center. “The nervous system tends to become hyperactive as nerves regain normal function.”
“The nerve structures, as they recover, tend to be irritable for a period of time. That’s because the nerves are firing spontaneously,” it continues. “It is a temporary phase that means nerves are coming back to life.”
Is it a problem?
Almost always, your limbs or extremities falling asleep like this isn’t a big problem. It’s got a simple cause, and a simple solution – and it should only last a short time.
“Most of the time, when your foot, or any other body part, falls asleep, it is temporary and nothing to worry about,” confirms Gillen. “In fact, since it lasts for only a minute or two, you may not even remember it happened by the end of the day.”
However, there are a few more concerning causes of numbness and other unusual sensations, in this case known as neuropathy. Actually, scratch that – there are a lot of potential causes: more than 100, affecting around 20 million people total.
“Diabetes is the most common identifiable cause of peripheral neuropathy, accounting for nearly a third of cases,” points out Robert Shmerling, former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center and senior faculty editor at Harvard Health Publishing. “Sometimes it’s the first indication that a person has diabetes.”
Similarly, it can be a symptom of diseases in the liver, kidney, or thyroid. It may be a sign of vascular disease, which can cut off blood supply to nerves and leave them unhealthy or even dead.
Otherwise, it could be something you ate – or didn’t eat. “Nutritional deficits, such as vitamin B12 deficiency or other vitamin deficiencies” may be to blame, Shmerling wrote in 2020, while “vitamin B6 is unique in this regard because too little or too much can cause neuropathy.”
“Too little is quite rare, but it’s possible to get excess B6 from supplements,” he explained.
Certain medications can cause numbness, as can toxins like lead or mercury. But perhaps the most likely culprit is something far more basic: “Alcohol ingestion is probably the most common cause of toxic neuropathy,” Shmerling wrote.
Not only can the alcohol itself cause nerve damage, but it can also interfere with nutrition – partly because it impedes the body’s ability to transport and absorb nutrients, and partly because, well, alcoholics often don’t look after their diets all that well. Malnutrition, again, leads to nutritional deficits, just compounding the problem. In fact, so connected is alcohol to nerve damage that almost half of the people who engage in chronic heavy alcohol use also report some kind of numbness in their body.
When you’re drunk, you’re also more likely to suffer what’s colloquially known as “Saturday Night Palsy” – a particularly severe form of this phenomenon, in which you fall asleep in a position that compresses a nerve, but because you’re drunk, you don’t wake up to remedy it. The result is a dead arm or leg that may last days or weeks rather than just a few moments.
If your slumbering limb isn’t covered by any of that, however – well, bad luck. “Nearly a third of cases have no clear cause,” Shmerling wrote. “When in doubt, see your doctor.”
How to treat it
If this numbness doesn’t go away promptly, it might be wise to seek medical help. “Call your doctor promptly if you have persistent numbness, tingling, or other unusual sensations in your hands or feet,” advised Shmerling. “This is especially important if these sensations cause trouble with walking or holding onto things.”
But assuming you just have a run-of-the-mill nerve compression issue, there’s not much to do. You can’t really avoid the odd dead leg or arm – evolution is imperfect; you’re going to occasionally sit still too long, or lie in bed too awkwardly, and find yourself with a weirdly numb appendage.
Luckily, it’s not harmful – and it’s easily remedied. “Once you start to move around again, the pressure on the nerves is released,” Gillen wrote. “They ‘wake up’ and you’ll start to notice a ‘pins and needles’ feeling.”
“Don’t worry,” he added. “That feeling will only last for a few minutes and then everything will feel normal again.”
All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.
The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.
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