Be more active when uneasy (8)

I believe the answer is:

restless

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'uneasy' is the definition.
(I know that uneasy can be written as restless)

'be more active' is the wordplay.
'be' becomes 'rest' (resting is a kind of being).
'more active' becomes 'less' (I can't explain this - if you can you should believe this answer much more).
'rest'+'less'='RESTLESS'

'when' acts as a link.

Can you help me to learn more?

(Other definitions for restless that I've seen before include "Fidgety - unable to sleep" , "Wakeful" , "Never still" , "Uneasy and agitated" , "Ceaselessly in motion" .)

I've seen this clue in the Evening Standard.

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