Ever wake up to a numb, dead arm? Here’s what’s happening.

This phenomenon is really common, says James Dyck, a neurology researcher with the Mayo Clinic. And it's actually a cool example of how the body can protect itself even during the paralysis of sleep.

Dyck explained there's a common misconception that pins and needles and numbness are caused by a lack of blood flow to the nerves. "The more likely thing is nerve compression — nerves are being pushed on and squashed, and that causes these symptoms," he says.