Fatigue turning into bout of fever (4-3)

I believe the answer is:

ague-fit

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'bout of fever' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'fatigue turning' is the wordplay.
'turning' is an anagram indicator.
'fatigue' is an anagram of 'AGUE-FIT'.

'into' is the link.

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