Antonyms for the phrase "weighed heavily on" might suggest a feeling of release or freedom. Synonyms for "weighed heavily on" include "burdened," "oppressed," and "troubled." Antonyms for this phrase could therefore include "lightened," "liberated," and "freed." Other antonyms might include "carefree," "easy," or "unencumbered." Conversely, synonyms for "weighed heavily on" might indicate a sense of importance or urgency. These could include "critical," "pressing," or "demanding." Antonyms for these words could include "insignificant," "trivial," or "unimportant.