You may feel numbness and other loss of sensitivity in the arms or legs (beside the typical pain) when your spinal cord or nerves are stuck or squashed. The numbness will usually occur in such regions that correspond with the supply area of each nerve root.
Based on so called dermatome, the doctor is able to make a diagnosis and conclude which nerve is affected.
Often nerve irritations manifest themselves also through unpleasant tingling/prickling as if a colony of ants would be going over the skin.
If the pressure of the nerve root is promptly removed, the nerves can mostly recover well and the symptoms disappear. However, when relief does not come in time, then the nerve is often permanently damaged. The patient then suffers from ongoing unpleasant sensations (tingling/prickling) or even numbness in the affected area.