Source : Webster's Revised Unabridged Dictionary (1913)

Fitful \Fit"ful\, a. [From 7th {Fit}.]
   Full of fits; irregularly variable; impulsive and unstable.

         After life's fitful fever, he sleeps well. --Shak.
   -- {Fit"ful*ly}, adv. -- {Fit"ful*ness}, n.

         The victorious trumpet peal Dies fitfully away.
                                                  --Macaulay.

Source : WordNet®

fitfully
     adv : in a fitful manner; "he slept fitfully"