Depressed following endless depression, depression (6)
I believe the answer is:
hollow
'depression' is the definition.
(hollow is a kind of depression)
'depressed following endless depression' is the wordplay.
'depressed' becomes 'low' ('low' can be a synonym of 'depressed').
'following' is a charade indicator (letters next to each other).
'endless depression' becomes 'hol' (I can't justify this - if you can you should give a lot more credence to this answer).
'low' after 'hol' is 'HOLLOW'.
Can you help me to learn more?
(Other definitions for hollow that I've seen before include "Cavity or space in something" , "Not solid or genuine" , "Dent; echoey" , "Concave; empty inside" , "Empty - hole" .)