Feeling sad (4,2,3,5)
I believe the answer is:
down in the mouth
'feeling sad' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for down in the mouth that I've seen before include "Miserable" , "Not happy" , "dejected?" , "evidence of poor pheasant plucking?" , "Unhappy (colloq.)" .)