Son flusters agitatedly, not relaxing (9)

I believe the answer is:

stressful

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'not relaxing' is the definition.
I can't tell whether this defines the answer.

'son flusters agitatedly' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'agitatedly' is an anagram indicator (I've seen this in other clues).
'flusters' with letters rearranged gives 'tressful'.
's'+'tressful'='STRESSFUL'

Can you help me to learn more?

(Other definitions for stressful that I've seen before include "tense" , "Very hard on the nerves" , "Worrying" , "under great pressure" , "Creating tension" .)

I've seen this clue in The Times.

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