Cuckoo let inside not even suffering after flight (3-6)
I believe the answer is:
jet-lagged
'suffering after flight' is the definition.
The definition suggests an adjective which matches the answer.
'cuckoo let inside not even' is the wordplay.
'cuckoo' indicates anagramming the letters (I've seen this in other clues).
'inside' means one lot of letters goes inside another.
'not even' becomes 'jagged' (I can't explain this - if you can you should believe this answer much more).
'let' anagrammed gives 'etl'.
'etl' put within 'jagged' is 'JET-LAGGED'.
Can you help me to learn more?
(Other definitions for jet-lagged that I've seen before include "Suffering from high-speed, long-distance air travel" , "Suffering from fatigue due to air travel" , "Tired from long-distance air travel" .)