Occasionally I'll wake up from a deep sleep and realize my arm has also fallen asleep. When it "wakes up," I do everything I can to keep still and control the almost unbearable sensation of "pins and needles."

There's actually a medical term for this called Transient Paresthesia. Usually, you feel this temporary yet bizarre sensation after you've been putting pressure on part of your body, like when you're sitting on a foot or sleeping on your arm. When you apply this pressure for a prolonged period of time, you actually cut off communication from your brain to parts of your body. This pressure squeezes nerve pathways so that the nerves can't transmit electrochemical impulses properly.

Nerve impulses carry sensation information from nerve endings in the body to the brain, as well as instructions from the brain to the rest of your body. The information transmitted from the "sleeping" body part becomes somewhat jumbled, and the brain receives strange messages. Some nerve cells don't transmit any information and others start sending impulses erratically. This causes you to feel a strange numbing, burning, prickly, or tingling sensation, which actually serves an important function. Your foot falling asleep for 10 minutes doesn't pose any health threat, but if you were to cut off circulation for an extended period of time -- several hours -- you could suffer serious nerve damage. The initial tingling sensation tells you that you might want to readjust your position.

Just thought you might want to know...

Source