Cheer up then crashing down? Not easily achieved (4-3)
I believe the answer is:
hard-won
'not easily achieved' is the definition.
(I've seen this before)
'cheer up then crashing down?' is the wordplay.
'cheer' becomes 'rah' (rah is a triumphant cry).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'then' is a charade indicator (letters next to each other).
'crashing' indicates anagramming the letters.
'rah' in reverse letter order is 'har'.
'down' is an anagram of 'dwon'.
'har'+'dwon'='HARD-WON'
(Other definitions for hard-won that I've seen before include "Gained with difficulty" , "Not easily achieved, took a lot of effort" , "Gained after much work and effort" , "Having been obtained with effort" .)