Hysteria essentially filling this writer's article (4)
I believe the answer is:
item
'article' is the definition.
(both can mean an object or thing)
'hysteria essentially filling this writer's' is the wordplay.
'essentially' means to look at the middle letters.
'filling' means one lot of letters goes inside another.
'this writer's' becomes 'I'm' ('I am' referring to the writer of the clue).
The centre of 'hysteria' is 'te'.
'te' put inside 'im' is 'ITEM'.
(Other definitions for item that I've seen before include "point" , "Time (anag.)" , "Seperate article in an enumeration" , "Whole individual unit" , "Report" .)