Ecstasy's opposite (5)
I believe the answer is:
agony
'ecstasy's opposite' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for agony that I've seen before include "Distress" , "Severe pain, mental or physical" , "Excruciating pain" , "Intense pain" , "Extreme suffering - kind of aunt" .)