* Tranquilo: This is the most direct opposite, meaning "calm" or "relaxed."
* Sereno: This emphasizes a state of peaceful composure and tranquility.
* Relajado: This emphasizes a state of being physically and mentally relaxed.
* Confianza: This emphasizes a feeling of self-assurance and trust.
* Seguro: This emphasizes a feeling of being confident and certain.
The best word to use will depend on the specific situation and the nuance you want to convey.