Final answer:
To regain feeling in a body part that has fallen asleep, gently scratching or massaging the area can stimulate the hair root plexus and sensory nerves, increasing blood flow and neural activity.
Step-by-step explanation:
If you experience numbness after falling asleep, gently scratching or massaging the affected area can help regain feeling more quickly. This sensation happens because the hair root plexus, which surrounds the base of the hair follicle, can sense changes in the environment and transmit this information to the central nervous system. The activation of these sensory nerve endings helps to 'wake up' the area by increasing blood flow and neural activity, thus alleviating the numbness.