Fits (6)
I believe the answer is:
spasms
'fits' is the definition.
(spasm can mean a fit)
This is all the clue.
(Other definitions for spasms that I've seen before include "attacks" , "Convulsions, fits" , "Nervous twitches and painful convulsions" , "Sudden muscular contractions" , "Sudden convulsions" .)