Antonyms for the phrase "weighing heavy upon" could include "lightening," "easing," "alleviating," or "releasing." These terms suggest a sense of relief or liberation, indicating that whatever was once a burden has been removed or reduced in some significant way. Other antonyms might include "lifting," "promoting," "encouraging," or "cheering," which all connote a sense of positivity and progress. Whatever the term, the overall sense is one of improvement, suggesting that the original weight has been lessened or eliminated entirely, leaving behind a feeling of freedom and ease.