Feeling tension's a disorder (9)
I believe the answer is:
sensation
'feeling' is the definition.
(sensation is a kind of feeling)
'tension's a disorder' is the wordplay.
'disorder' is an anagram indicator (I've seen 'diseased' mean this (I've seen this in other clues)).
'tensions'+'a'='tensionsa'
'tensionsa' anagrammed gives 'SENSATION'.
(Other definitions for sensation that I've seen before include "Feeling produced by stimulation, or dramatic news (9)" , "Feeling, awareness of stimulation" , "Physical feeling or perception" , "Scandal" , "Crowd puller" .)