Restlessness shown by Ms Rykiel engaging medium (8)

I believe the answer is:

insomnia

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'restlessness' is the definition.
(thesaurus)

I cannot understand how the remainder of the clue works.

(Other definitions for insomnia that I've seen before include "Wakefulness" , "State of chronic sleeplessness" , "Sleep disorder" , "Habitual inability to sleep (8)" , "Habitual sleeplessness" .)

I've seen this clue in The Telegraph.

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