Go to bed in rough sea, gloomy (9)
I believe the answer is:
saturnine
'gloomy' is the definition.
(thesaurus)
'go to bed in rough sea' is the wordplay.
'go to bed' becomes 'turnin' ('turn in' can be a synonym of 'go to bed').
'in' indicates putting letters inside.
'rough' indicates an anagram.
'sea' anagrammed gives 'sae'.
'turnin' going inside 'sae' is 'SATURNINE'.
(Other definitions for saturnine that I've seen before include "Gloomy (temperament)" , "moody" , "dull" , "offering little amusement" , "may be brooding" .)