General antonyms:
* Sadly
* Sorrowfully
* Regretfully
* Mournfully
* Gloomily
* Dejectedly
* Despondently
* Angrily
* Frustratedly
* Reluctantly
More specific antonyms depending on context:
* If it's about celebration: Grimly, solemnly, reluctantly
* If it's about a positive experience: Painfully, miserably, reluctantly
* If it's about a sense of lightness: Heavily, burdenedly, anxiously
The best antonym will depend on the specific situation and the meaning you want to convey.