Sid signed off, getting dizzy spells (9)
I believe the answer is:
giddiness
'getting dizzy spells' is the definition.
(getting dizzy or giddy)
'sid signed off' is the wordplay.
'off' indicates anagramming the letters.
'sid'+'signed'='sidsigned'
'sidsigned' is an anagram of 'GIDDINESS'.
(Other definitions for giddiness that I've seen before include "State of excitable frivolity" , "Vertigo" , "Excitability and frivolity" .)