The phrase "were beside oneself" refers to a state of extreme emotional turmoil or agitation. Antonyms for this phrase would include being calm, composed, or collected. If someone is calm, they are not agitated or anxious, and may instead feel peaceful, relaxed, or content. Someone who is collected is in control of their emotions and thoughts, able to remain calm and focused in the face of challenges or stressors. And someone who is composed is self-assured, confident, and unruffled, able to maintain their poise even in difficult or trying circumstances. All of these antonyms for "were beside oneself" suggest a state of inner strength, emotional stability, and psychological resilience.