Brief sleep that is never-ending (7)
I believe the answer is:
dossier
'brief' is the definition.
(both can mean a collection of information)
'sleep that is never-ending' is the wordplay.
'sleep' becomes 'doss' (to doss is to sleep in an improvised bed).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'ending' suggests the final letters (the ending of the word).
The final letter of 'never' is 'r'.
'doss'+'ie'+'r'='DOSSIER'
(Other definitions for dossier that I've seen before include "Papers containing detailed information about someone" , "brief" , "File of papers (sometimes dodgy)" , "File of documents" , "Set of papers" .)