Flexi Says: When an arm, leg, or other body part "falls asleep," you may experience numbness and a tingling sensation as feeling returns. The medical term for this condition is called paresthesia, and it is typically a temporary condition. It is caused when a nerve traveling to the affected area of the body is compressed or under pressure. This can happen when you are sitting or sleeping in one position for a long time. The pressure on the nerve prevents it from properly sending signals. The condition will usually resolve in several minutes after changing position or moving the affected area.