Feeling 'Pins and Needles' Is a Circulation Problem
A tingling or numb sensation in the muscles is a condition called paresthesia. It's a sign that a nerve is irritated. Think of that pins-and-needles feeling as a traffic jam in your nervous system.
When traffic is running smoothly, tiny electrical impulses move along the nerves that run from your spine to your arms and legs. These sensations then move up the spinal cord to the brain.
But if sustained pressure is placed on a nerve, you create a roadblock that prevents the nervous system from carrying the electrical impulses that normally transmit feeling.
While the nerve is compressed, so are the arteries that feed blood to the nerve. The nerve can't function for long without a consistent supply of oxygen and glucose. Interfering with the nerve's ability to send signals or with its blood supply causes a limb to "fall asleep."
For example, people in wheelchairs who sit for long periods of time are more prone to nerve "traffic jams." When the blockage is removed, the nerve cells begin waking up as they start receiving impulses again. You may begin to feel an uncomfortable pins-and-needles sensation. 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. Most of the time, the irritability--the feeling of pins and needles--is a good sign, a temporary phase that means nerves are coming back to life.
In some cases, however, a nerve may be seriously injured, perhaps in an accident. Then the nerve may get stuck in a pins-and-needles stage and the person may experience continuous pain. A good example is carpal tunnel syndrome. In this instance, "pins and needles" can be a danger signal. Most often, though, "pins and needles" is just an odd but harmless sensation that we feel from time to time.