Where one might stay depressed (4)
I believe the answer is:
flat
'depressed' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for flat that I've seen before include "character on the staff" , "Unnatural - uninteresting - apartment" , "not deep?" , "Level; pad" , "Like a pancake?" .)