Isn't oneself (4)
(Other definitions for ails that I've seen before include "Is unwell - sail away" , "Is not well" , "languishes" , "Feels unwell" , "Troubles; afflicts" .)
'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" .)