Uneasy, lacking sleep (8)
I believe the answer is:
restless
'uneasy' is the definition.
(I know that uneasy can be written as restless)
'lacking sleep' is the wordplay.
I cannot really understand how this works, but
'lacking' could be 'less' (I've seen this in another clue) and 'less' is present in the answer.
'sleep' could be 'rest' (synonyms) and 'rest' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for restless that I've seen before include "Unable to settle" , "Constantly moving about or fidgeting" , "Ill at ease" , "Unsettled, fidgety" , "Fidgety - unable to sleep" .)