There are several antonyms for the word "unburdened." One of them is "burdened," which means weighed down or encumbered by a heavy load or responsibility. Another antonym is "stressed," which refers to feeling overwhelmed, anxious or tense due to mental or emotional pressures. "Worried" is another antonym, meaning feeling anxious or concerned about someone or something. "Preoccupied" is yet another antonym, describing being absorbed or engrossed in something to the extent that one is unaware of their surroundings. Essentially, any term that describes something that is the opposite of being free of worry, problems, or responsibility would be an antonym for unburdened.