Composer ill in bed, endlessly sick (7)
I believe the answer is:
bellini
'composer' is the definition.
(I've seen this before)
'ill in bed endlessly sick' is the wordplay.
'endlessly' means to remove the last letter.
'sick' is an anagram indicator.
'ill'+'in'+'bed'='illinbed'
'illinbed' with its final letter taken away is 'illinbe'.
'illinbe' is an anagram of 'BELLINI'.
(Other definitions for bellini that I've seen before include "Italian opera composer (Norma)" , "Musical artist" , "He made a lot of notes" , "Champagne and peach cocktail" , "Peach juice cocktail" .)