In total sobriety as well (4)
I believe the answer is:
also
'as well' is the definition.
(synonyms)
'in total sobriety' is the wordplay.
'in' indicates a hidden word.
'ALSO' is hidden in the letters of 'total sobriety'.
(Other definitions for also that I've seen before include "Likewise" , "Plus" , "Item" , "As well, in addition" , "in accompaniment" .)