Being uneasy, suffer a reduction in sleep (8)
I believe the answer is:
restless
'being uneasy' is the definition.
('restless' can be a synonym of 'uneasy')
'suffer a reduction in sleep' is the wordplay.
I cannot quite understand how this works, but
'sleep' could be 'rest' (synonyms) and 'rest' is found in the answer.
The remaining letters 'less' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for restless that I've seen before include "Uneasy and agitated" , "Constantly moving about or fidgeting" , "Unable to relax or be still" , "Fidgetty" , "Worried and uneasy" .)