I saw a man at the Hollywood Roosevelt with a numb arm. That’s an odd complaint but unlikely to represent something serious in a 26 year-old.
He’d fallen asleep on the plane, resting his head on his palm with an elbow on the arm rest. On awakening he felt numbness down his forearm. This was easy.
The ulnar nerve that supplies the hand passes under your medial epicondyle, the knob you can feel inside your elbow. It’s a poor design because the nerve runs near the surface. Injuring it produces tingling down your arm to the little finger. It’s the “funny bone.”
Cab drivers who spend the day with one arm resting on the door often complain of numbness. Once they stop doing this, the discomfort disappears.