Synonyms:
* Disheartened: Feeling a loss of courage or hope.
* Dejected: Feeling low in spirits; depressed.
* Disappointed: Feeling let down or sad because something did not meet expectations.
* Appalled: Feeling horror or disgust.
* Aghast: Feeling shocked and horrified.
* Despondent: Feeling very sad and without hope.
Antonyms:
* Encouraged: Feeling hopeful and confident.
* Elated: Feeling very happy and excited.
* Joyful: Feeling great happiness and pleasure.
* Hopeful: Feeling optimistic about the future.
* Reassured: Feeling confident and certain.
* Thrilled: Feeling very excited and happy.
The best synonym or antonym for "dismayed" will depend on the specific context in which it is used.