You've been curled up on the couch for a whole movie with one leg tucked under you. You stand up, and your foot is a useless, rubbery lump. A few seconds later, the fizzing starts, as if a thousand tiny needles are poking you from the inside. It's funny and maddening at the same time. So what's going on?
Here's the short answer: when you lean or sit on part of your body for a while, the steady pressure on your nerves interferes with the signals they carry. The limb goes numb, or falls asleep. When you move and the pressure lifts, those nerves start firing again, and the tingling, prickly feeling as they recover is pins and needles. Once the pressure is gone, it usually fades gradually on its own.
There's a Word for a Sleeping Foot
Doctors call a limb that falls asleep obdormition, from the Latin word obdormire, meaning to fall asleep. It's temporary numbness, often caused by constant pressure on nerves or by not moving for a long time.
The tingling that follows has its own name: paresthesia. It can feel like numbness, tingling, pricking, chilling, or burning. It's usually painless, and while it can happen anywhere on the body, it shows up most often in the arms and legs.
Your Nerves Under Pressure
Think of your nerves as cables carrying messages between your body and your brain. Squeeze a cable long enough and the messages start getting scrambled. Sustained pressure over a nerve can block or stir up its signals.
Most of these episodes come from awkward posture. Sitting cross-legged for a long stretch is a classic cause, and so is resting your head on your arm or leaning on your legs. The fix is usually simple: change position, and the feeling soon passes.
Blood flow can play a role, too. When blood rushes back into an area after it's been cut off, tingling can come along with it. People with Raynaud's disease, for example, may feel it when their fingers warm up after a cold spell.
The Funny Bone Is a Cousin
That zap you feel when you bang your elbow is part of the same family of sensations. The funny bone isn't a bone at all. It's the ulnar nerve, which runs past the elbow trapped between the bone and the skin, with very little padding to protect it.
The nickname is thought to be a pun on the humerus, the bone of the upper arm, which sounds a lot like humorous. Another explanation is that funny simply describes the peculiar feeling you get when you hit it.
There's an even stranger relative called formication: the feeling of insects crawling on or under the skin when none are there. The word comes from formica, the Latin word for ant.
When to Pay Attention
An occasional sleepy foot after sitting oddly is completely normal. Tingling that keeps coming back, lingers, or shows up for no clear reason is different, because it can have many possible causes, from poor circulation to diabetes or a vitamin shortage. If that sounds familiar, talk to your doctor.
For the everyday kind, though, there's nothing to fear. That fizzy rush is simply your nerves clocking back in after an unscheduled nap. Give your foot a minute, and it'll be ready to walk you to the kitchen for more popcorn.
