You've had your legs crossed for too long and you've whacked your elbow on something hard - welcome to Pins and Needles City, population: you. But what causes that uncanny sensation of having unbearable tingling and numbness all at the same time? Most of us assume it's a lack of blood flow to the area, because the feeling of pins and needles most commonly originates from when we put pressure on and don't move a particular body part for an extended period of time, but as the latest episode of SciShow explains above, blood flow is only half the story.

Known formally as paraesthesia, pins and needles occurs when you interfere with your body's sensory nerves by restricting their blood supply, which means they can't get the oxygen and energy they need to continue sending signals to your brain about the things you're touching. This will cause that feeling of numbness, which will only go away once you uncross your legs or start moving again. And then comes the fun part: the horrible, overwhelming tingling.

The tingling is caused when your nerves are suddenly given access to blood again, and that all excitement causes them to misfire as they reboot, which the brain interprets as pins and needles. 

The other way you can give yourself pins and needles is by putting pressure on a nerve, because this also restricts blood flow to the tissues surrounding it. A classic example is when you smack your funny bone, and basically ruin your own life for the next 60 seconds. The reason your elbow in particular causes this sensation is because it's connected to the ulnar nerve, which runs from your neck to your hands, and is particularly exposed and vulnerable in the elbow region, says Hank Green in the video above.

But having pins and needles isn't that bad, because at least the feeling only lasts one or two minutes, right? Well, in some very unfortunate cases, that tingling sensation can stick around for days. DAYS. And the same thing can happen if a person experiences major nerve damage, has a tumour pressing on their nerves, or has a nervous system disorder such as multiple sclerosis.

So how do you get rid of pins and needles? I'll let Hank reveal that little secret in the SciShow episode above, but let's just say you're gonna have to be okay with looking like an idiot until it's all over. But hey, no more tingling is worth it, right?