Unwell in a way relatable to the pulse? (5)

I believe the answer is:

seedy

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'unwell' is the definition.
(thesaurus)

I don't understand the rest of the clue.

(Other definitions for seedy that I've seen before include "Unpleasant" , "Pip is" , "Shabby and a bit dubious" , "sickly" , "Sleazy, sordid" .)

I've seen this clue in the Evening Standard.

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