A tingling or numb sensation is a condition called paresthesia. It’s a sign that a nerve is irritated and transmitting extra signals. 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 constant pressure is placed on a nerve, it causes a roadblock. This prevents the nervous system from carrying the electrical impulses that normally transmit feeling.
Paresthesia can result from many different causes and can be temporary (reversible) or permanent, usually from nerve, spinal cord, or brain damage.
While the nerve is squeezed, so are the arteries that feed blood to the nerve. The nerve can't work for long without a steady supply of oxygen and glucose. Anything that gets in the way of 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 start 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 feeling of pins and needles is a good sign. It is a temporary phase that means nerves are coming back to life.
Paresthesia can be felt in people who have an implanted spinal cord or peripheral nerve stimulator.
In some cases, a nerve may be seriously injured, perhaps in an accident. Then the nerve may get stuck in a pins-and-needles stage. And you may experience constant pain. A good example is carpal tunnel syndrome or diabetic neuropathy. In these instances, “pins and needles” can be a danger signal. Paresthesia that happens with other symptoms may also indicate an underlying condition. Most often, though, “pins and needles” is just an odd, but harmless, sensation that we feel from time to time.