Antonyms (opposite meanings):
* Calm: Serene, tranquil, composed, peaceful
* Unfazed: Unconcerned, indifferent, nonchalant
* Relaxed: At ease, comfortable, carefree
* Tranquil: Peaceful, serene, quiet
Synonyms (similar meanings):
* Disturbed: Upset, agitated, troubled
* Anxious: Worried, uneasy, apprehensive
* Alarmed: Frightened, scared, startled
* Concerned: Worried, apprehensive, troubled
* Disquieted: Uneasy, troubled, disturbed
The best synonym or antonym to use will depend on the specific context of the sentence.