Air travel fatigue (6)
(Other definitions for jetlag that I've seen before include "feeling of disorientation" , "sickness from being transported" .)
'air travel fatigue' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for jet lag that I've seen before include "Delayed tiredness after long flight by air" , "Tiredness and disorientation after long plane journey" , "Flyer's ailment" , "Bad effect of air travel" , "Tiredness felt after long plane flight" .)