Initially mysterious pseudonyms shifting one's anxious feelings (8)

I believe the answer is:

malaises

'anxious feelings' is the definition.
(a malaise is an anxious or uncomfortable feeling)

'initially mysterious pseudonyms shifting one's' is the wordplay.
I cannot quite understand how this works, but
'one's' could be 'is' (Roman numeral) and 'is' is found in the answer.
This explanation may well be incorrect...

I've seen this clue in The Independent.

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