Jet Leg usually occurs near the end of a crowded Southwest Airlines flight. You're packed in like sardines and you haven't moved your legs for 3 hours. When you get up to exit the plane, your legs are asleep and are cramping up something fierce. Jet Leg is not contagious and usually subsides somewhere near the baggage terminal. 'Jet Leg' is the evil step-sister of 'Jet Lag'.
Rawd: "John, how was your trip and why are you limping"?
John: "I have a terrble case of Jet Leg, Rawd"
Rawd: "Don't you mean Jet Lag"?
John: " No, Jet Leg, Rawd. Jet Leg!!