Sodium to handle a sickness (6)
I believe the answer is:
nausea
'sickness' is the definition.
(I know that sickness can be written as nausea)
'sodium to handle a' is the wordplay.
'sodium' becomes 'NA' (chemical symbol).
'to handle' becomes 'use' ('use' can be a synonym of 'handle').
'na'+'use'+'a'='NAUSEA'
(Other definitions for nausea that I've seen before include "A feeling of disgust or illness" , "Squeamishness" , "Queasy feeling" , "Sensation of queasiness" , "Seasickness" .)