Synonyms for Spasmodic (same or very similar meaning)
WordNet sense 1 (affected by involuntary jerky muscular contractions; resembling a spasm):
convulsiveWordNet sense 2 (subject to change or variation):
unsteadyWordNet sense 3 (occurring in spells and often abruptly):
fitfulWordNet sense 4 (recurring in scattered and irregular or unpredictable instances):
sporadicFrom the ODE community, based on WordNetadd/edit