Fatigue following a long flight (6)
(Other definitions for jet lag that I've seen before include "Tiredness felt after long plane flight" , "Discomfort due to changing time zones when flying" , "traveller's complaint" , "Feeling of tiredness after long air flight" , "Air traveller's malaise" .)
(Other definitions for jetlag that I've seen before include "feeling of disorientation" , "sickness from being transported" .)