Maybe insomniac struggles without whiskey and splash of soda? (8)
I believe the answer is:
restless
'maybe insomniac' is the definition.
'struggles without whiskey and splash of soda?' is the wordplay.
'struggles' becomes 'wrestles' (wrestle is a kind of struggle).
'without' is a deletion indicator.
'whiskey' becomes 'w' (alpha bravo charlie delta ...).
'and' means one lot of letters go next to another.
'splash of soda?' becomes 's' (I can't explain this - if you can you should believe this answer much more).
'wrestles' with 'w' taken away is 'restles'.
'restles'+'s'='RESTLESS'
(Other definitions for restless that I've seen before include "Uneasy and agitated" , "Fidgety - unable to sleep" , "Always on the move" , "Worried and uneasy" , "Uneasy, unable to relax" .)