Singer gets crazy on sodium (7)
I believe the answer is:
madonna
'singer' is the definition.
(American singer)
'crazy on sodium' is the wordplay.
'crazy' becomes 'mad' (synonyms).
'sodium' becomes 'NA' (chemical symbol).
'mad'+'on'+'na'='MADONNA'
'gets' acts as a link.
(Other definitions for madonna that I've seen before include "Lady - type of 1 across" , "pop star" , "religious painting" , "Virgin Mary - or American showbiz queen" , "Guy's girl" .)