Synonyms for Drowsy (same or very similar meaning)
WordNet sense 1 (half asleep):
dozy, drowsingWordNet sense 2 (in a state of sleep):
asleepWordNet sense 3 (showing lack of attention or boredom):
oscitant, yawningWordNet sense 4 (showing a lack of attention or care):
inattentiveFrom the ODE community, based on WordNetadd/edit