Sex up left-winger, getting exhausted (5)
I believe the answer is:
tired
'exhausted' is the definition.
(exhausted can mean very tired)
'sex up left-winger getting' is the wordplay.
'sex' becomes 'it' (a common euphemism).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'left-winger' becomes 'red' (red can mean a leftwing person).
'getting' says to put letters next to each other.
'it' reversed gives 'ti'.
'ti'+'red'='TIRED'
(Other definitions for tired that I've seen before include "In need of rest" , "Dressed once" , "Physically or mental weary" , "Weary, jaded" , "Sleepy" .)