When we stay in one position for long time, our arms or feet tend to fall asleep. We begin to feel a tingling sensation and find ourselves unable to move that part of body. Though it is widely believed that our limbs fall asleep when they do not get blood supply owing to the pressure put on them but the fact is that it is not blood circulation but nerves which are responsible for this break.
In fact, when we exert some pressure on that particular limb, we inadvertently tend to block the nerve pathway. Since these nerve pathways do not get to communicate the message of brain to the limb, that limb falls asleep in absence of communication from the master mind.
When you ease off the pressure from that part, the nerves slowly begin to resume their work and the messages begin to get transmit to that part of body. When the nerves reactivate the messaging system, they create this tingling, pin and needle sensation in that body part. Once proper communication is established, the tingling sensation vanishes away.
This sensation is an indication that something is not right in the body. Hence when you begin to feel uncomfortable about this sensation, you try to fix it by shaking your limbs and everything sets right. The clinical term for this condition is Paresthesia.
Sometimes Paresthesia is a result of some serious health problem like multiple sclerosis or neuropathy. But these conditions are rare. The transient pins and needles sensation can be resolved by simply shifting the weight of your body parts from one side to other and by shaking your limbs for a couple of minutes.