Isn't oneself (4)

I think it could be either:

ails

acts

'isn't oneself?' is the definition.
(I've seen this in another clue)

This is all the clue.

(Other definitions for acts that I've seen before include "5th NT book" , "Biblical book" , "exerts influence" , "Dramatic parts" , "Cast in major divisions of plays, like Shakespeare's" .)

I've seen this clue in The New York Times, the Newsday.com and the Newsday.

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