Refusal to get up — those folk stop getting better (2,3,4)
I believe the answer is:
on the mend
'getting better' is the definition.
(I've seen this in another clue)
'refusal to get up those folk stop' is the wordplay.
'refusal' becomes 'no'.
'to get up' is a reversal indicator.
'those folk' becomes 'them' (I've seen this in another clue).
'stop' becomes 'end' (synonyms).
'no' backwards is 'on'.
'on'+'them'+'end'='ON THE MEND'
(Other definitions for on the mend that I've seen before include "undergoing recovery?" , "convalescing" , "Becoming better in health" , "Informally getting better, improving after illness or accident" , "Improving in health" .)