1. To happen or to develop more slowly than expected or wanted; Production was continually lagging far behind demand at the factory.
2. Hanging back or falling behind: Jeremy kept lagging behind the rest of the hikers because he lacked the necessary stamina to keep up with them.

Descriptive of being very tired and lacking physical energy after a long flight: Walter's jet lagged sister had to recuperate and readjust to her normal life after her flight home from Canada back to Germany.