The Collaborative International Dictionary of English v.0.48:

Fitful \Fit"ful\, a. [From 7th Fit.]
   Full of fits; irregularly variable; impulsive and unstable.
   [1913 Webster]

         After life's fitful fever, he sleeps well. --Shak.
   -- Fit"ful*ly, adv. -- Fit"ful*ness, n.
   [1913 Webster]

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

WordNet (r) 3.0 (2006):

fitfully
    adv 1: in a fitful manner; "he slept fitfully"

Moby Thesaurus II by Grady Ward, 1.0:

65 Moby Thesaurus words for "fitfully":
   at haphazard, at intervals, at irregular intervals, at random,
   brokenly, by catches, by chance, by fits, by jerks, by skips,
   by snatches, capriciously, carelessly, desultorily, disconnectedly,
   discontinuously, eccentrically, erratically, flutteringly,
   haltingly, haphazardly, here and there, hit or miss, in snatches,
   in spots, inconstantly, indiscriminately, infrequently,
   intermittently, irregularly, jerkily, lurchingly, nonuniformly,
   occasionally, off and on, patchily, per saltum, promiscuously,
   quakingly, quaveringly, quiveringly, randomly, roughly,
   saltatorily, shakily, shudderingly, skippingly, sloppily,
   spasmodically, sporadically, spottily, tremblingly, tremulously,
   uncertainly, unevenly, unmethodically, unpredictably,
   unrhythmically, unsteadily, unsystematically, variably, waveringly,
   whimsically, willy-nilly, wobblingly